There are loads of places in and around Trafalgar Square in London where you can get a quick and cheap bite to eat, both eat in and takeaway. Below are some well known chains that are within walking distance, including Pret A Manger, Caffe Nero, Little Frankies, Tesco and Wagamama:
For more info on how popular meal deals are in the UK, check out this article in The Sun newspaper.
also, this article in the Daily Mail is about cheap and healthy supermarket meals
Right next door to The Admiralty pub is a branch of Pret A Manger who do a large range of ready made wraps, baguettes, salads, soups and drinks at reasonable prices, they have interesting toppings like 'beetroot and radish on rye'.
To the left of Pret A Manger is a Caffe Nero, which is an Italian style cafe serving coffee, cakes and more.
Just across the road is a sit down restaurant called Little Frankies, the style is New York Italian, and they offer a wide range of casual Italian food. Open from early til late you can get breakfast for £3.95 and lunch for £6.95 or a two course dinner for £9.95. Little Frankies also have 50% off deals at various times, some of which require you to sign up on their website in advance.
Little Frankies
Little Frankies is only two doors down from the Tesco Express on Charing Cross Road. Tesco is also a great option for takeaway lunch or dinner. They have a dinner meal deal that serves two people for £10, with your choice of a main, side, desert and bottle of wine or other drink.
Tesco also has loads of lunch deal options for just £3 that include a main, snack and drink - a great option to pick up before heading off to the Chelsea Flower show or to do other sightseeing. Conveniently the Charing Cross Road Tesco is open 24 hours a day.
Another great option for fresh and tasty food is Wagamama. This Asian Fusion chain has a restaurant located just a 400 metre walk north of the apartment, at 9 Irving street. They serve ramen, curries, teppanyaki and donburi, cooked fresh to order.
Of course because Trafalgar Square is so centrally located there are a lot more options within walking distance, including international chains like Burger King and McDonalds.
Hopefully the above info will give you a good idea about what it will cost to eat in a restaurant or get takeaway, so that you can plan ahead how much money you will need for food during your time in London.
For some information I have prepared on Supermarket basics for self catering click here