Note, there are at least 4 speed cameras between the M1 and the sports centre... All 40 limits.

Also to note, its easiest to go anti-clockwise around the magic roundabout from this direction.

Those travelling clock-wise on the M25, take J20, then A41 to Hemel Hempstead Exit.
Continue straight until the magic roundabout. Turn left onto A4146 (left then left).
Keep in the left lane then take the next right (before the church on your right) onto St. Johns Road.
Take your second turning on the right onto Heath Lane.
You are now passing the sports centre.