Thanks for your replies. Quidhampton sidings are at the junction of the Western and Southern lines on the Warminster side of Salisbury at Wilton. I understand the sidings use the former Western lines from Wilton to Salisbury after the track layout was rationalised many years ago.
All traffic now uses the former Southern lines dividing at Wilton for Warminster or Tisbury. The sidings are controlled by a ground frame.
They are disused as in there is no traffic, however they are used for occasional stabling purposes.
The last train out was empty tanks to Tavistock Junction, the last regular service was the trip to Eastleigh. The reason for the cessation in traffic was the refusal of the planning authority to extend the Quarry.
But, i wonder if the area around Quidhampton Sidings could be used for a station serving the Wilton area? Wilton Parkway? That way, it could be served by the several Exeter / Gillingham bound SWT Services, as well as picking up traffic on the FGW route too - most notably, the Southampton Central terminators, or by increasing the Trans Wilts service to a regular Salisbury to Swindon service? and act as a Park & Ride for that end of Salisbury...