You need to define you needs a little better. For example, a nice penlight would be the Lumintop IYP365 or one of the other IYP variations.
A nice shirt or pant pocket would be the Lumintop Tool 2.0 AA. I run a 14500 cell in mine for the extra output, but it is adequate just using an AA primary. For more of a thrower you have the Lumintop GT Mini and Micro. Both are under your £50 limit as well. The Mini uses an 18650 Li-Ion cell, and the Micro uses a 14500 Li-Ion.
I own at least one example of each of these models and love them. The Tools usually ride in my jeans pocket, and I just got some really nice holsters for the GT Mini and GT Micro from Nealsdeals, along with a nice diffuser for the Mini.