THis is overwhelming, so many fascinating suggestions. I was going to look at the Rick Steves book, plus what they do on his tours, but I probably have enough information here to research.
Mileage tickets are crazy cheap. 33K round trip from the states on Delta, upgraded to Economy comfort. I’ve used more than that on a one way ticket from SEA to SFO before. Now if only they didn’t charge such high taxes out of Europe.
Attending a session of Parliament could be amazing…especially if they actually do swear at each other and throw things. 
“Now if only they didn’t charge such high taxes out of Europe.”
The UK charges a substantial departure tax unlike other European countries. If you feel like a couple of days in another country (e.g. Eurostar to Paris) and fly back direct from there at the end, you can avoid those taxes.
If you have time, take a tour from London to Stratford-upon-Avon, where Shakespeare lived and lots of 16th century Tudor architecture remains. You could book in advance to get tickets for a play at the Royal Shakespeare Theatre.
Parliament was, indeed, entertaining!
If any of your family members enjoy soccer, watch a Premier League game in person.
We stayed in Mayfair which was very easy to walk to Hyde Park, the palace and Bond Street shopping. We were right by the American Embassy. But I usually travel on Marriott points so I stay where I can use my points. However if you could stay by the eye, London Tower, etc I think that would be an even better location.
FWIW there are fares to Scotland for $300-400 right now on KLM, Delta and Air France. Mostly May but some in April and Jan/Feb.
Someone above mentioned how easy it was to get theater tickets, I’d like to add that they are cheaper than the broadway theater prices, I just looked on ticketmaster uk and Hamilton orchestra tix are 100 pound. I paid $800 for my NY Hamilton performance.
Rick Steves’ London guidebook is an excellent purchase to read ahead of time and take with you. A lot of info on websites as well.
@sly123 We had a discussion with the young woman working at the discount ticket booth about the cost of shows in the US. She says there are folks from NY who fly to London just to see Hamilton. They can get a vacation PLUS the show for the cost of show tickets in NY. Doesn’t quite work that way coming from the west coast - plus the flights just too long.
We lived in London for 3 years in the late ‘90s. We were there when Diana died. We had many visitors, so I went to many of the tourist sites multiple times. The Tower is by far and away my favorite place in London. I never tire visiting it. Get to the Tower early and do the Crown Jewels first. There is never any line early. Then, find out when a Yeoman Warder is giving a tour and join it. They will not take you everywhere, but they are lots of fun. There is a nice lunch place within the Tower, so you can stop for lunch or a cup of tea and a pastry.
There is a London Pass that I think is worth it. It is good for most attractions in London and gives you a discount on souvenirs at most places. It even gives you a discount at the Tower restaurant. There is also a Thames riverboat ride included. You can get a 1,2,3,6 or 10 day pass. It is good at Windsor Castle and Hampton Court Palace, too. They are nice out of London day trips.
When we were in London in Oct. 2017, we stayed at the St. Ermin’s Hotel. It was in the Victoria Station vicinity. It was a 5 minute walk to Westminster Abbey, and around the corner from St James Park tube station. It is a lovely hotel that is in the Marriott autograph group. Our aunt used her Marriott points for our nights there.
You have to get to Harrod’s and see the food court. Our aunt loved it. It really is an amazing place.
You can get half priced theatre tickets in Leicester Square. We saw many great shows that way.
If you pay for my ticket, I would be happy to be a personal tour guide. I love London. We are going for Christmas. Our D3 lives there and this is the first Christmas we have been back.
We went to Ireland and England. We had private drivers . We went to bath and Cornwall. Also London. Go to Windsor castle for sure.
My daughter lives in London, but we do not get there as often as I would like. We both had big birthdays last year, so along with my son and DIL, we went for a visit. For my actually birthday, we spend the night at The Pig near Bath. We had a wonderful stay along with dinner in the hotel and toured the garden and grounds the next day. https://www.thepighotel.com/near-bath/
We spent a good part of the day at the Roman Bath and had planned to go to the Thermae Bath Spa, but it was so windy and cold, we decided to bail on the trip. It was a nice one day/one night trip; worth the trip if you have the time.
It will be a fun family trip!
I had a son who went to school in England and always we always enjoyed our side visits to London. On our last stay, it was both of us and our two boys. We stayed at the Citadines apartment hotel in Trafalgar square. (10% off if you join their membership club) We got a 2 story 2 bedroom unit with a living room/dining room and kitchette. It was great to have breakfast foods and evening snack/beverages readily available. It was perfect for us, but you may also opt for a 1 bedroom for the parents and put the kids into a studio. Our 2 bed looked just like the photo, but I don’t know if all of them are the same.
When I was first looking at hotels, I sort of blew off this one because I just wasn’t sure of the location, but we all agreed we would return! https://www.citadines.com/united-kingdom/london/citadines-trafalgar-square-london/index.html?utm_source=google&utm_medium=gmb&utm_campaign=CitadinesTrafalgarSquareLondon
The hotel was moments from Charing Cross train station, right next to Sherlock Holmes pub, a Marks and Spencer food/liquor store, Trafalgar Square and the theater district, Picadilly Circus, etc. Taking the Picadilly line from Heathrow it is one tube change or depending upon luggage you could walk from Leicester Square. I think the ride was about 6 or 7 pounds because the airport is outside the central zone. Get an Oyster card for each of you and you can start with maybe 10 or 15 pounds until your get a feel for how much you will be riding.
The previous posters are spot on regarding amazing places to visit. We discovered the Borough covered Market http://boroughmarket.org.uk I have never seen such a huge display of fabulous foods. We filled our tummies and then took the river walk down to and then across the London Bridge over to the Tower of London.
I also think Windsor is a great place to visit and an easy train ride.
Take a look at the viator.com website for London and then “day trips” just to get a feel for what is doable.
I think that was a joke about how some people are reacting to Brexit.
I lived in England for 20 years. March is going to be wet and chilly. Having said that, it’s a good time to visit in terms of seeing tourist sites. Bring proper rain jackets and appropriate footwear.
Around London:
Get the guide book, Hidden London. Full of cool little tidbits of info. Check things off as you see them. Fun.
If you plan to visit the Harry Potter Warner Brother’s studio tour, you might find my review helpful: https://www.tripadvisor.com/ShowUserReviews-g2691242-d2147749-r305532757-Warner_Bros_Studio_Tour_London_The_Making_of_Harry_Potter-Leavesden_Hertfordshi.html
Have tea one afternoon in London. You can spend a FORTUNE, or a lot less. If you want posh, got to Fortnum and Mason. I love, love, love that store, and I think it’s a million times better than Harrod’s. You can get the most amazing picnic/gift baskets there, in all price ranges. Buy handmade marshmallows in exotic flavors. They are delectable. My kids ask my husband to bring some home every time he goes to the UK for work.
I HIGHLY recommend you visit Churchill’s War Rooms. That’s my new favorite attraction in London. Within 2 hours of London, the best places to visit, IMO, are Bath, Cambridge, Hampton Court Palace, Hever Castle, Warwick Castle, Battle, and Brighton (and the Brighton Pavilion.)
Cornwall and Devon are gorgeous, but at that time of year, I’m not sure it’s worth visiting. You could do the hike to Land’s End though, which will go along the coast and should be very beautiful.
If you are including regions north of, well, the South and Southwest, Edinburgh is wonderful. You could go to the Highlands, which will probably feel wonderfully desolate. I love the area around the Yorkshire Dales and Durham. The Lake District is absolutely beautiful with lots of great hiking, but in March, I don’t know if it’s a must do. But there is so much to see that you might just have to brave it. I also love the Peak District. I love Chester, and the Cathedral there is amazing. The high street is filled with shops tucked away in genuine Tudor buildings.
Whatever you do, be sure to get out of London and see the countryside. There is something very special about driving around the winding country lanes, shielded by hedgerows on both sides, and wondering if another car is coming around the bend. Find some country pubs with a fire and have a Ploughman’s Lunch. Wander into a tea room and get a Bakewell Tart or a Flapjack, and a cuppa. Have a wonderful trip!
^^^^^ Oooh - Bakewell Tarts!!! I frequently travel solo and often find myself eating in the venues I’m visiting. The museum cafe/cafeterias often have a great selection of traditional English pastries as well as good, traditional hot food offerings. I remember the Tate Britain and Imperial War Museum cafeteria in particular from 2016 trip. Bletchley Park cafeteria served food typical of what the WWII code breakers would have found.
I haven’t read the thread but wanted to mention that after South Africa, England is my parents’ favorite country, and they’ve been to many countries. 
I get to go to London with my folks next summer, because my dad (at 82) will be speaking at an engineering conference.
We loved the little town of Bakewell. So beautiful, with lots of interesting castles around it. Flowers EVERYWHERE, and a little river running through town. I would love to go back there. Loved the Tower of London, too.
the London dungeon is really fun, I believe it is near the London eye.