Halfords: Carrera - "up to 80 miles" on a 36v 9aH battery? Is that really feasible?!You could consider this as well......
http://www.halfords.com/cycling/bikes/electric-bikes/carrera-crossfire-e-mens-electric-bike
It states 9ah battery but a poster on here has just bought one and it actually comes with an 11ah battery. Also has hydraulic disc brakes and different frame sizes. It'll be heavier than the Karoo but it'll be a more comfortable ride.
Also its easy to go back to Halfords if there's any problems with it...... plus you may get a discount on it by joining British Cycling Membership.