Did a quick bit of research on Google; the Mi-2 I spotted was SP-SWG and can be seen at
this link on Air Britain's website. Amazing what you can find on line.
I had thought it was here for a month or two, perhaps PZL/WSK used it for a marketing opportunity with the various UK companies while it was here, which might explain its presence over the SE. I don't think I've ever seen another one.
I remember there were some Polish fixed-wing aircraft at Farnborough that year which was around the same time.