Nobody seems to have mentioned the turntable at Wansford on the Nene Valley Railway.
I saw it in action quite a few years ago, and it's still being used - see this extract from the NVR web site:
The Turntable
"The turntable, located behind the new station building, was built by Ransomes & Rapier of Ipswich in 1933. Originally 60 foot long it was installed at Bourne in Lincolnshire for use on the Midland & Great Northern Joint Railway. In 1959, Bourne shed closed and the turntable was moved to Peterborough East; its last duties being to turn Travelling Post Office (TPO) coaches for use on the East Anglian TPO.
In 1977 the turntable moved to Wansford where it was extended to 76 foot and was re-commissioned in September 1978. The turntable has been in use ever since to turn the locomotives and carriages at the NVR."
Here (hopefully!) is a link to the Google Maps page which shows it:
https://www.google.co.uk/maps/place...efe2de1d96d8dd5!8m2!3d52.5694985!4d-0.2405299