Steve, what Pete says is valid. The new releases played at Cleethorpes in the mid 70s fitted in alongside the 60s music. It was with the late 70s and 80s releases that the change came about... and that change was in tempo. The watered down, mid-tempo stuff is what gets overplayed at so called ATB nights now, because it's easy for the obese or over-fortified "soulie" to shuffle along to, and that's one reason why some have moved towards 60s events.
Incidentally, it's interesting to see some enlightened folks calling for "truely across the board" music policies, encompassing the five decades of soul music, etc etc, as long as there's no shite R&B played... kinda negates the whole noble ideaology, surely?