The Home Counties--All those Counties around London- are pretty flat. If you want FLAT-flat then go to Essex where speed bumps are the high points of a ride.
But South of London there are two Chalk ridges called the Downs running East to West. The North Downs are about 25 miles South of London and are about 1,000ft down into the next valley. The hill on the Olympic course-Box Hill- is on the North Downs and the road is about 5 to 10% gradient. The South Downs are not quite as high at 800ft but they are steeper. Length is not as much but there are plenty of 12 to 15% climbs for 1 mile that go either straight over or drop from the top of the downs down to the rivers along the ridge. My avatar is taken at the top of a 3/4 mile hill along the ridge.
Couple of pics of the Offroad route and a Profile map of the same. The "slippage" area is where I was going too slow to register on the Garmin and it then caught up with itself. The road routes are just a bit less steep but not by much.
The bikes were provided by one of their suppliers and 20 in number. Only 8 were taken up by the staff so 12 brand new Raleigh Hybrids still in the boxes to go back or they will be sold off to staff as we have convinced them that an organised 100 mile ride for charity could be done later in the year "IF THEY TRAIN FOR IT"
But at the current rate--There will still be 12 bikes going back