I've got some Continental tires on my old mountain bike which I use for commuting on the road. Not sure which ones, but they're 1.5" wide. They'll take 80-90 psi no problem, and I've used them for 3 years with no flats, of course that could just be luck. But I would think the Specialized, or most other brands are pretty much equal.
Another point to consider is how much are you going to use them after the London - Brighton, if you're just buying them for that ride then get something cheap with no tread. And speaking of tread if you're using them only on the road then no tread is better, think baby bottom smooth.