Generally any £100 android phone will be a pig to use.
There are a couple of options though that if you search around you may be able to find for there or there about. Orange San Francisco 2 or the Motorola Razr i.
Or, look on ebay for a second hand Samsung Galaxy SII – still a very good phone.
The final Android option is to look at some of the Chinese handsets. Google is your friend here (as are fellow STW’s) as some are apparently brilliant and others are dogs.
Alternatively the Nokia Lumia 520 running WinPho 8 runs very smoothly and most major apps are now available (Instagram being the big omission at the moment but there are 3rd party alternatives).