The last generation GM5 were almost the definitive English Ceilidh band - and will be considered even the more so after their dispersal in 1996.
The Gas Mark V of the CD Jump! sought to bring an eclectic mix of music into high energy whole, the result made for a some excellent tunes and a lively dance. With Guizers that music has fused, is more laid back, and appears with a greater swing - having a saxophone in the line-up has a lot to do with this. Gas Mark V were a worthy successor to the highly esteemed, but sadly demised, Ran Tan Band.
It probably was the definitive Ceilidh band for experienced dancers, ones who do not need a foursquare fixed beat to fit their feet to. Gas Mark V didn't necessarily give this, the rhythm is looser, and thus requires more thinking when dancing.
For more details and a more definitive history, Trevor Bennett has put together the Stories and Histories of Gas Mark 5 (now on the wayback machine).
Gas Mark V, 1988, Festival C2, Cassette only.
Gas Mark V, 1991, Regul02 CD, Regular Records
Gas Mark V, 1994, Regul03 CD, Regular Records