A very quick explanation: The X-Wing, DV Tie, R2, C-3PO and DV were produced in 1978 by MPC in America. Also some SW van kits. Dennis Fisher released all but the DV and the vans in Britain. I have seen German language Kenner versions of the X-Wing and C-3PO. Dennis Fisher later released The Millennium Falcon from MPC.
For ESB Palitoy issued the Millennium Falcon, Star Destroyer and Snow Speeder.
Airfix was bought by General Mills and handed over to Palitoy which released Airfix packaging versions of Snowspeeder, AT-AT, Slave One, Star Destroyer, Rebel Base diorama, Hoth Attack diorama, Dagobagh, Millennium Falcon and the X-Wing. For ROTJ: Shuttle Tydirium, Speeder Bike, Jabba's Palace, AT-ST and the four piece pack containing snapfix X-Wing, TIE Interceptor, B-Wing and A-Wing. The snapfix Y-Wing came out in America but not by Airfix.
C-3PO and R2-D2 are listed in "The Boy's Book of Airfix" as having been released in 1985 by Airfix but I have never seen them.
There are tons of American box variations, gold kit editions, free flight stands, you name it. There were some rubbish kits called, I believe the "Structors" that were clockwork including AT-ST and C-3PO. Also some even more rubbish "Mirror Kits" where you only got half of a model and a mirror to stick it on to, making it appear whole.
Later we got snapfix versions of the TIE Fighter in the scale of the TIE Interceptor (two in the box) and some kits from "Shadows of the Empire." Ertl bought out MPC in 1985 so all SW kits were labelled accordingly from then on.
The pics are of my MPC and Revell Y-Wings. They are both in the same scale, only the smaller MPC one was based on the under-scale studio prop and the Revell on the true life scale.
If anyone wants to talk about Star Wars kits - the scale issues especially, I'm your man!
Craig.