Time of day makes an enormous difference. It's 0753 on Tuesday morning and I'm at the cafe at High Street Kensington, just hanging out here until about 0930 when I have to get the Tube out to Heathrow.

Right now £1 ($1.45) buys 2.5 hours. The best I've done between London and Glasgow cafes this last week, going later in the morning, has been about 75 minutes for £1, but on the other hand you're not likely to see me out the door at 7 in the morning when I am on vacation to take advantage of the additional time offered this early.