For £100 you’re not going to get a top notch drill, or more correctly top notch batteries. I’d steer well clear of the £99 Makitas, they’re general NiCd batteries and not good value for money. A £99 Ryobi with a 1.4ah LI-ion battery is better value. I’ve two Ryobi drills and an angle grinder, they’re fine. 1.4ah battery is a bit weak but you can also buy a 2.4 ah battery and recently they’ve released a 4ah monster battery.
I’ve also got an extremely good Hitachi with 3.6ah 18V batteries but that was £300 quid.
Edit rwc03, looks a good deal for an 18V 3.0ah LI-ion battery
All depends on how much you intend to use it.