631 was the first of a batch of 10 Sunbeam S7A trolleybuses which entered service in Huddersfield in November/December 1959 to replace some of the ageing rebuilt Karrier E6 trolleybuses. These were Huddersfield’s last new trolleybuses and also the last three-axle trolleybuses built for service in the United Kingdom. They followed the style of the previous Huddersfield trolleybuses (3-axle, double-deck, 7' 6" wide) to fit in with the rest of the fleet, despite the regulations having been relaxed a few years earlier which would have enabled these trolleybuses to have been built as two-axle. They were not particularly well-liked by the Huddersfield crews, who tried to have alternative vehicles allocated to them.
631 led an uneventful life during its 9 years in service. However, when the trolleybus system in Huddersfield was abandoned in July 1968 the Huddersfield Trolleybus Preservation Society (HTPS) secured 631 for preservation. She was used for two very successful enthusiast tours of other systems before she was 'retired' to museum work. On 27 October 1968 631 toured the Reading system with Belfast 168 and she ran another tour in Bournemouth on 24 November 1968.
631 was transferred to the site which became the Trolleybus Museum At Sandtoft in 1969. Following the demise of West Yorkshire Transport Circle (one of the groups which grew out of the HTPS) 631 was transferred to BTS ownership. Arguably 631 has been Sandtoft's most reliable service trolleybus over the years and is still in good condition.
In 2012 631 was decorated in true Huddersfield style to mark the Queens Diamond Jubilee. On 10 January 2013 631 was towed to Swindon where she was externally repainted back into Huddersfield livery and also a partial internal repaint.was carried out. The seating was re-upholstered too. On 3 May 2014 631 was returned to Sandtoft and she will be recommissioned into service later in 2014.