Bike advice

sadly the OP said it's over his price range.

I'll have you know that all of my suggestions were out of the given price range :)

secondly if you only use 3 to 5 gear on your mountain bike, then you'd get used to a single speed bicycles easily, riding MTB on road isn't exactly easy especially with MTB tyres, so a singlespeed bicycles will likely to feel a LOTS easier to ride than an geared MTB.

best option? go to your local Evans and test ride the Charge Plug, to see whether you'd want to go down that road or not.

best way to decided if the bike is for you is to simply test them out.

Yeah, totally agree.

Still lots to decide though....

If want something easy to ride like a hybrid theres always the centrum sport (cheap too).
http://www.evanscycles.com/products/specialized/centrum-sport-2008-hybrid-bike-ec001472

Or could go cyclocross, with the specilized tricross.
http://www.evanscycles.com/products/specialized/tricross-singlespeed-2009-road-bike-ec016875

or MTB with something like the GT peacemaker
http://www.evanscycles.com/products/gt/peace-2008-single-speed-mountain-bike-ec000676

or road bike ie. Gary fisher triton.
http://www.evanscycles.com/products/gary-fisher/triton-2009-single-speed-road-bike-ec017199

More here:
http://www.londonfgss.com/thread9085.html

All of these bikes have horzintal drop-outs, so if you find yourself wantin gears in the future. You can simply buy a Hub gear, and rebuild your back wheel. Hub gears are great for bikes that are used everyday in all conditions.