Luckely, London is one time zone away, so my flying time will only be five minutes, giving me always three hours between landing and the start of the conference. Hopefully, that gives me enough leeway to be there on time to give my talks.
BTW, if you are reasonably paranoid, don't fly British Airways and order your ticket over the internet. It's all convenient and such, but a bit too convenient for the security aware. They'll give you a URL where you can change your flight details. No authentication required. And they send the URL by email. Unencrypted. With a warning not to forward the email.