London hotels, no matter what chain, are
expensive, full stop. Even a grotty two-star hotel is around £100/night - that's about $175. The only bonus is that most hotels (though not some of the US chains, eg Hilton, Radisson etc) include breakfast. And hotels in London are generally not as good as elsewhere: smaller rooms, poorer service, staff who tend not to speak English very well and so on.
Just about all the big hotels - even three-star ones, such as the Holiday Inn Express - have conference facilities. So your attendees would stay at the same hotel where the conference is taking place.
The alternative, though, for the sort of conference you're talking about would be to hold it at a university. All British universities (probably universities the world over) offer conference facilities out of term-time, and sometimes inside term-time (believe me, I've fought with University conference people over normal access to teaching rooms on occasion!). So university conference facilities might well be cheaper than hotels. In a university you'd get a large lecture theatre (or more than one, if required), and several smaller seminar rooms for smaller workshops, plus a big mezzanine area for tea/coffee. Having been to academic conferences in many unversities in the UK, it all seems to be pretty similar.
To save further on costs, your attendees could stay in university accommodation - again, these days just about any university which takes conferencing seriously will offer new or newly-refurbished rooms with en-suite facilities. Or you could simply use a local 2- or 3-star hotel.
What universities could you use? I've been in conferences at UCL (University College London), KCL (King's College London), Imperial, the London School of Economics (a bit drab) and one or two others. There's also the University of Westminster, London Metropolitan University, Goldsmith's College and several others. I haven't had time to give you the home page for all of these universities, but they're very easy to look up on Google. Every UK university address ends in .ac.uk, though, so UCL would be
www.ucl.ac.uk. Hope this helps.
Wendy
