It was not only the married/attached couples who were affected by the rules.
In Tengah in the 60's one of the Sqn Flt Lt Navs married a civilian girl, and held the reception in the Officers Mess. The whole aircrew contingent were invited, and attended in uniform. That is apart from the two NCO navigators who were given special permission to attend in civilian clothes! However it was normal for several Junior Officers to attend the Sgts Mess Happy Hour on Friday nights in uniform!
At Marham in the late 60's the Plt Off Copilot on my crew had his Father and Mother living on camp at the same time. As the father was a Master Pilot they were not able to go to each others Messes, and the Copilot was not supposed to visit his parents in their MQ.
On a slightly different tack, one of the Nav students at Hullavington was entertaining a Cpl WRAF PTI in his room at night. When she went down the corridor to the toilet, she met the Queen Bee coming out of a male officer's bedroom. Nothing was said!