London is big. Really very big and very spread out. A travel agent or web site may say a hotel in Sydenham is "central", but this just means it's not as far as Surrey.
Another caveat is that Hotels in London tend to be expensive. Often more that the US counterparts. Do not be surprised to see rates of £100-200 per night. Also make sure you get the price with taxes included. This is especially important since tax (VAT) rates are 17.5%.
In order to make your life easier we've found some places that are reasonably priced and actually centrally located and convenient for both touristy things and the big event itself.
Club Quarters is not a hotel so much as a private club. Members get a decent, central, and nice place to stay in London when traveling on business. Since the hotel is across the street from the wedding venue, they are allowing our guests to stay there at member rates. While for weekdays the rates are fairly comparable to many London hotels, on weekends they're quite cheap, going from £49 per room and up.
If you want to book a room, you need to read the instructions. Most important is that you mention the member company: Stationers Hall. However, if you work for one of their member companies, you might be able to get a cheaper rate. So if you think you might, make sure you ask.
Check in is at 3pm. Check out is at noon. yuo should be able to negotiate these times if you need to.
Niceties include
Club Quarters has informal relations with child-minders who can look after young children and infants. If you want your child looked after during the wedding, let us know the number of children and their ages. However, if you do not wish to leave your infant with the child-minder, you may bring them to the wedding. We need to have firm numbers before 18 Dec to make arrangements. We can also provide their contact details for you to use at other times during your stay.
At this point in time we've not actually checked out any of these places: caveat emptor
London Bed and Breakfast Agency was recommended by a friend. We've not used, so be warned.
These places just provide you with a place to stay, usually with bedding and towels. Many have their own kitchens and such. They don't clean up after you. Think of it as a very short leased apartment.