Traveling to London in March

Buy an Oyster card for transportation on the Tube and buses; refill as needed. It will take you all over London.
Buy a guide book! Top sites to visit include Westminster Abbey, Churchill War Rooms, Buckingham Palace, Tower of London, British Museum, Tate Gallery snd much more.
Day trips to consider are Windsor Castle, Oxford, and Cambridge.

Since you will really only have about 4.5 days of availability, I would Google things to do in London and see what interests you both. Unless you have a very specific place in mind to see on a day trip, I would stick to London proper. The underground is economical and even though I have not stayed in one, it appears from this forum Premier Inns are nice places to stay. Enjoy a very historical London. Also, many museums are free.

it appears from this forum Premier Inns are nice places to stay.

I wouldn't describe Premier Inns as nice places to stay. What they are are clean, functional, basic but with good beds at reasonable rates. There are plenty of nice places to stay at in London, a Premier Inn is a safe bet for those who want a decent but basic room at a decent price.

For the OP, you barely have any time for London so I wouldn't even entertain the idea of a day trip. The time it takes to travel is time that can be used more efficiently in London.

I agree about day-trips; there's way too much to see in London to leave the city on a first visit of only 4 non-jetlagged days.

Get a guidebook specifically for London; Rick's is good and very detailed, with a lot of excellent logistical advice that will help you be efficient sightseers. Make a list of places you'd both like to see. If you don't seem to have enough common goals you can split up for part of the time to focus on individual interests. Think about what places you might want to visit only if you're lucky with the weather; stay as flexible as you can, except for sights needing advance-purchased tickets.

If you enjoy walking and the weather's decent, the just-show-up 2-hour walking tours offered by LondonWslks are a fabulous value at £10. There are dozens and dozens of them. The winter schedule won't be available until this fall, but you can take a look now at the summer offerings, many of which will be offered during your timeframe.

Come back here with your list of potential sights and we'll warn you about tickets needed ahead of time, etc. Your list may also suggest that it would be good to stay in a particular part of town, though it's probably more likely that your sightseeing targets will be scattered.

You can use booking.com for a preliminary idea about lodging costs; the reviews are relatively trustworthy, and you can go to the hotel's website to make your reservation if you prefer to do so.

I find the Premier Inns generally reliable (check rates on the corporate website, premierinn.co.uk) and used them heavily this summer when I had a roommate to share the cost (as you do) and wanted to be sure of air conditioning (which you certainly will not need). Outside of air conditioning season, there will be less-expensive options, but recognize that lodging costs in London are very, very high, so it will probably seem that you're not getting much for your money. Do look at photos on booking.com (and maybe also TripAdvisor) so you know what you're getting--often a tiny room with an even tinier bathroom and charmless, dorm-like decor. There are still some hotels in London with bathrooms down the hall. They are less expensive. If you want to avoid those, the term to look for is "en suite bath".

1.) Buy the RS London Guidebook. Read it! VERY insightful and practical info to help you plan your first trip to London!
2.) Make a list of what you MUST see.
3.) Book your rooms at The Victoria Premiere Inn which is a 10 minute walk from Victoria Station and where the Gatwick Express arrives. Quiet neighborhood but so convenient.
4.) As noted you’ll barely have time to explore London so think of day trips on your next visit.
5.) Forget the Changing of the Guards. Over rated and under whelming.
6.) when you arrive at Gatwick or at Victoria station get an Oyster card for each of you. It’s your key to the city
7.) Thousands of cafes and restaurants in London. You won’t starve.

Pub grub is fine. There will be sign boards on the sidewalks displaying lunch offerings. In March you’ll appreciate the soups and stews that will be offered on menus in pubs, cafes and restaurants.

If looking for freshly made sandwiches, salads and soups look for Pret A Mangers. Nandos chicken is a popular chain. Bill’s restaurants are good. Food at the markets ( Portabello best on Saturday, Camden Lock, Borough ) are also good.

8.) Pack lightly. Good all weather waterproof coat/jacket. Comfortable worn in shoes. As Walking is the best way to explore London.

9.) Dress in layers

10.)Apple pay is big there but I still use a coin purse to carry a few pounds.

Great city!!!! Have fun!!!! Don’t try to see it all. You’ll return!

Your post makes me think you are not going anywhere else in Europe. Airfare is expensive, you'll be paying a lot for not much time. Is there any way you can stay longer? Why so short?

There's no time for day trips. Find somewhere near Westminster to stay if you can. On one of our trips, we stayed at the Hilton Westminster and it was very convenient, within walking distance of Parliament, Downing Street, Westminster Abbey, etc. The last time we were there we stayed in Marylebone, which was 10-15 minutes from Westminster via the Underground.

I agree that changing of the guard is a waste of time. The one daytrip you might want to consider is Windsor Castle.

Use google maps to create a map of places you want to see in London - then, when you view the map, you can group places near eachother instead of wasting a day on the tube. For example - London Eye + Imperial War Museum (both on the Southern side of the Thames).

What are your interests? I love the National Gallery but if you have no interest in European painting, it would be pointless to go there.

I wouldn’t even consider a day trip with that short of time and since it’s your first time.

I agree completely with the suggestion of Premier Inn as a place to stay. But, keep in mind, they’re a chain so think more of Courtyard by Marriott as opposed to Ye Olde Cute and Quaint. Again, more information on your tastes would be helpful.

You can eat everything from a McDonald’s to a £200 steak dinner in London, so you’ve got endless choices. I agree with the recommendation of Pret A Manger, even if you’ve been to one in the USA, the menu is completely different in the UK. Good sandwiches and hot food as well, they also do excellent breakfast food if you’re not getting breakfast at the hotel. If you like Mexican, I’d suggest Wahaca, it’s a small chain with very good Mexican food. I also like Bil’s, it’s another small chain with a bit of something for everyone.

But, unless you’re looking for Michelin caliber restaurants, it’s easy enough to walk around and find something you like. I honestly believe you can find any single cuisine in the world available in London.

Since you are flying into and out of Gatwick, your roundtrip tickets on the Gatwick Express (or the less expensive Southern train service) will serve to qualify you for the 2-4- 1 offers with Days Out:

https://www.daysoutguide.co.uk/travel-by-train/is-my-ticket-valid-for-2for1

This means you and your friend can visit many of London’s best attractions together with one paid entry. To qualify, you must buy both the inbound and outbound tickets for Gatwick and be able to show them at the ticket office for each site. This means you must hold on to your inbound tickets (heading TO Victoria station) instead of going through the regular turnstiles to exit the station. The regular turnstiles will retain your ticket as you exit. Instead, look for the manned exit point used by wheelchair users and others with large bags. Simply explain that you need to retain your ticket and they will let you through.

You will also need a pre-printed voucher for each separate attraction. You can either print them out at home from the website before you leave, or hope you can find one of the little booklets full of vouchers at a london train station. I like to print them out at home as sometimes the voucher booklets are hard to find. You only need one voucher for the two of you (but you both need to show your train tickets).

The one downside to the 2-4-1 deal is that you must stand in the ticket queue at each attraction; you cannot purchase skip the line or timed entry tickets online and use the 2-4-1 offer. This can be a problem at highly popular sites like the Churchill War Rooms in the height of the tourist season, but it may not be an issue in March.

Have fun. We will be in London in March ourselves, but not our first visit; more like our 5th or 6th. (I have lost count).

I forgot to mention dining. For a nice economical sit-down dinner, we like the early dining/pre-theatre menu at Cote Brasserie. This is a chain and there are several in London. ( WE have dined at both the Covent Garden and Hays Galleria venues). You get a nice French-inspired 2-course dinner for under 13 GBP; a bit more if you want the 3-course dinner including dessert.