Try
NN12 8XA this puts you in Church Street, track entrance is between the village and West End (road name) on the north side of Church Street, on the right driving out of the village (west).
Maps on club site here:
http://www.srcmcc.com/where.html
"SRCMCC are based in the sports hall which is part of Silverstone Recreational Association Sports and Social club. The Pavilion and Sports club are situated off the main A43 on the other side of the village to Silverstone racing circuit. Follow the Whittlebury Road into Church Street. Take the road that goes round the Shop. The hall is near some swings, Football pitches, Tennis courts and the village Cricket ground."
So head into the village from A43 and look for the rec. parking on the grass near track (at least was last year) drive
around the edge of the cricket pitch. Toilets in pavilion/sports club, walk back across the pitch.