@Beachbum
Thanks very much, that does clarify things totally. Looking at the alignments with Topp's Cafe, the lift and the Royal Victoria Pavillion (Wetherspoons) it looks to be slightly further NE than the current roundabout. There is a curved feature centered at 100' NE at 51.33233002861004, 1.4240012779674762. GSV (Aug 2018) shows this as a funfair, but the current satellite view (2022) shows scrub land. Is this not more likely than the traffic roundabout at 51.33250047522633, 1.4244373818746219?
Anyhow, thanks for the help,Martin
EDIT: On further viewing I think the turntable must have occupied just the NE half of the traffic roundabout and extended into the scrub. There's no trace left on the satellite view though, so a few yards doesn't matter. M.