From junction 15 of the M4 take the A346 towards Marlborough.
As you enter Marlborough, turn right onto the A4 and continue along Marlborough High Street. At the end of the High Street the road bends sharply right and then sharply left (past Marlborough College). Stay on the A4 for approximately 1 mile. Keep going past signs for Manton Village and Manton House. Elm Tree Park is on your right-hand side (opposite first signpost for Clatford) and there is a ghost-island in the road to allow you to safely turn right. If you get to Fyfield (and the Murco garage) you've gone too far.
As you come up the drive into Elm Tree Park turn right, C Force Communications are the building on your left at the end of the road.