This is the Imperial Land Raider from August 1988 – released in the RTB5 box (two came in that box) and the RTB11 box (one came in that one).
White Dwarf 104 (Aug ’88) has them for £12.99, available late summer.
White Dwarf 170 (Feb 1994) states that it’s a new release as a boxed set for £12.99. Was it discontinued for a spell? Or is that just a re-release?
This is the best condition one I could find locally; it’s missing a few parts, unfortunately.
It’s also in need of a good clean and strip.