Theres a decent Hill of sorts on the Common at Hampstead.
From the bottom of East heath road where it meets South End Road cycle 1/3rd of way up before taking a right hander at a Y fork in cycle track & then go down hill between highgate ponds to millfield lane turn round at the gate and cycle all the way back up to Spaniards Road gate & turn round and go back down to the start on east heath road. You cant get lost its the only cycle route signed on the common, theres a 12 MPH speed limit as well but theres so much other shit going on around and about the last thing any one cares about is some one going fast on a bike.
I used to complete 6 Reps of that route and it takes about 15 mins per shuttle at a fair pace, its about as hilly as you are going to get, i think the point on Spaniards Road where the gate acces is located is the highest point in ye-Olde london Village.