Update...
MOT ran out just before lockdown, so left the bike scorned. On Tuesday took it for a test at the same garage, failed on squared off rear tyre, no mention of play in swinging arm.
I had loosened the pivot and greased where I could without dismantling fully, the torqued it up, still slight play.
I had actually thought of removing the centre stand! That would have made sure they couldn't have checked it.
Back this morning for a retest.