To reach London, you have essentially five airports to choose from: Heathrow (LHR), City (LCY), Gatwick (LGW), Luton (LTN) and Stansted (STN). All of them provide train service for reaching Central London, which can cost anywhere between a few pounds (e.g. taking the tube from Heathrow) and £20 (e.g. taking the Heathrow Express to Paddington or the Stansted Express to Liverpool Street). Most flights from outside Europe land at Heathrow.
Tip for arrivals at Heathrow: If you take the Heathrow Express to Paddington Station, be aware that Paddington has two separate Underground stations. The one you probably want for getting to UCL is located outdoors, not underground. (You might in any case be better off avoiding the Heathrow Express and just taking the Picadilly Line from Heathrow.)
Tip for arrivals at Gatwick: You probably want to take the train from Gatwick to St. Pancras Station, which normally costs between £10 and £13. Do not take the (more expensive) Gatwick Express unless you have some particular reason to go to Victoria Station.
Tip for arrivals at Stansted: The Stansted Express can be much cheaper(!) if you buy your ticket more than 30 days ahead of time, e.g. £16 instead of £35 for a return ticket from Stansted to London Liverpool Street Station. You can buy tickets online at www.stanstedexpress.com.
For participants arriving by train, UCL is within walking distance of Euston, King's Cross and St. Pancras Stations. (The latter is where the Eurostar from France/Belgium terminates; note that Eurostar tickets can be surprisingly inexpensive if bought far enough in advance!)
Most workshop participants will be housed within walking distance of UCL, but if you intend to use the London Underground more than twice during your stay (e.g. Wednesday afternoon is free...), you can probably save money by buying an Oyster Card. These are available from ticket agents at most Underground stations. More information on public transportation in London may be found at www.tfl.gov.uk. In particular, here is a standard tube map.
The talks will take place in the Harrie Massey Lecture Theatre on the ground floor of the UCL Department of Mathematics, located at 25 Gordon Street in Bloomsbury, Central London (see map below). Registration and coffee breaks will take place in the Wilkins North Cloisters, which is in a neighbouring building. UPDATE: Some talks will not be in Harrie Massey Lecture Theatre, due to problems with the air conditioning. See the main page for up-to-date announcements.
UPDATE 18/07/2014:
Directions to the Wilkins North Cloisters (registration): If you enter the UCL campus from the main gate on Gower Street (between Gower Place and Torrington Place), walk across the main quad and veer diagonally left. At the back left corner of the quad, you will find two doors with signs that say Wilkins Building - North Cloisters. The registration table will be through those doors.
Alternatively, if you're approaching UCL from the other direction (e.g. from Russell Square), you might find it quicker to go to 25 Gordon Street, enter the rear courtyard from Gower Place and then reverse the directions given below for getting from the North Cloisters to Harrie Massey Lecture Theatre.
Please note: The front entrance to the UCL Mathematics department at 25 Gordon Street is currently blocked off due to construction. You will have to enter the building from the rear courtyard, which is accessible from Gower Place (just around the corner from the 25 Gordon Street entrance).
Directions from the North Cloisters to Harrie Massey Lecture Theatre (lectures): From the North Cloisters, enter the stairwell next to the sign that says "Physics Building". Go down the stairs and exit the building, then round the corner to your right. You will find yourself in a courtyard somewhat lacking in ambience, but you should also see the words Harrie Massey Lecture Theatre on a building across the courtyard (to the left of the Physics Building).
The nearest underground stations to UCL Maths are Euston Square (Hammersmith & City, Circle, and Metropolitan lines), Euston (Victoria and Northern lines), and King's Cross / St. Pancras (Victoria, Northern, Picadilly, Hammersmith & City, Circle, and Metropolitan lines). Some of the hotels and student residences might also be closer to Russell Square (Picadilly line), Goodge Street (Northern line) or Warren Street (Northern and Victoria lines).
Unless you are a speaker or are receiving financial support to attend, we ask you to book your own accommodation. Here is a list of hotels near UCL (there are quite many). A potentially much cheaper option is to book a room in a UCL Student Residence.
Scheduling note: The workshop will begin Monday morning and end on Friday in the late afternoon, so it's best to plan on arriving by Sunday night and leaving Saturday.