This locomotive, built by Aveling & Porter, Rochester, Kent, who are better known for their traction engines, it is a "cousin" of Quainton's Sydenham.

The Blue Circle is a 2-2-0 well tank, class TJ, built to a design dating back almost 100 years. The locomotive was built in 1926, although at least 80 years out of date by that time. She is the very last traction engine type railway locomotive to be built on the 4' 8½" standard gauge.

Delivered new to Holborough Cement Co. Ltd., Kent (later to become Blue Circle Cement) for use at their Snodland Works.

Withdrawn in 1962 and presented to the Bluebell Railway when she was named The Blue Circle after her previous owners. She lay derelict for many years but then underwent heavy boiler repairs and then spent some time at the Northants Ironstone Trust as she was not really suitable for work at the Bluebell.

She arrived at Quainton as a working engine in 1997, having been presented to a QRS member on long term loan. She was later purchased by him and saw much service on freight trains in the downyard.   The Blue Circle had a makeover to appear as Thomas character Fergus for a visit to the Bluebell Railway in June 2004, returning to Quainton in this livery for the Thomas event at Quainton in November 2004.  The engine then left Quainton in March 2005 for the Chinnor and Princess Risborough Railway.

This locomotive form an interesting link with Quainton Road Station in that the Brill Tramway was worked by two Aveling & Porter locomotives between 1872 and 1894, one of which is now in the London Transport Museum, Covent Garden London, and is currently on loan to Quainton. The Blue Circle is believed to be one of only two working Aveling & Porter traction engine locomotive types on rails.