any manufaturers 'DIY' range are carp. they wont put up with normal use, never mind the abuse i expect my tools to put up with. (for example, undoing shock mounts with a 1" breaker bar... with a scaffold pole on the end.)
so you can be sure any tool i reccommend will be very rugged. but usually have a price tag to suit.
and on that note...
http://www.screwfix.com/p/makita-bhp459rfe-18v-3ah-li-ion-cordless-combi-drill-brushless-motor/35380
you wont do better than one of those.
however. if you dont need the runtime (and torque)...
http://www.screwfix.com/p/makita-bhp453sh-18v-1-3ah-li-ion-cordless-combi-drill/58614
same drill, damn sight cheaper.