Take the M40 out of London, pick up the M25. (Watford direction) and continue as per directions from M25.  See map.

OR exit Junction 1 of the M40. Follow A40 towards Denham/Amersham turn right at set of traffic lights, A412 signposted Watford, Rickmansworth.

Continue for about 3 miles until you come to mini roundabout. Turn right and continue as per directions from M25.