Looks quite easy Stu. The AA site gave me these directions and says about 1hr for me, so 30-40mins for you I guess.
Follow A23 as per CR but stay on left to join the M23.
Leave M23 at Junct 8 and join M25 - follow signs for Heathrow.
Leave M25 at junct 11 (signposted Woking A230, Chertsey A317)
At roundabout take 1st exit on to St. Peter's Way (A230 signposted Woking)
At roundabout take 3rd exit on to Guilford Road (A320 signposted Chertsey, Staines)
At roundabout take 1st exit on to Holloway Hill (B386 signposted Windlesham)
At roundabout take 3rd exit on to Chobham Lane (signposted Egham)
Or [url]http://www.surreyleague.co.uk/courses/modchertsey.htm[/url]
See you there