This was one of the must-have stocking-stuffers of 1978 (along with the Palitoy figures and - lets be honest - anything else adorned with the STAR WARS logo): the first STAR WARS ANNUAL, published by MARVEL UK.
Behind this rather striking (and somewhat off-model) cover was a seriously truncated version of Marvel's movie adaptation, ruthlessly edited to condense the entire US six-parter (already seen on this side of the Atlantic in the two 1977 Treasury Editions and the first twelve issues of STAR WARS WEEKLY earlier in '78) into one standard-length annual and STILL leave room for some behind-the-scenes features on the film itself.
Why did this appear in 1978 and not a year earlier? The movie didn't premiere in the UK until 27 December 1977 and, although some products appeared earlier (notably the aforementioned US treasuries, the paperback and the soundtrack), Marvel obviously decided to wait rather than release what was, essentially, an unproven product into the pre-Christmas market.
The annuals continued to appear right through to the 1985 edition which, in a sign of the times, had to share its pages with reprints of the Star Comics EWOKS strips, derived from the animated series.
Marvel always suffered from a dearth of fresh Star Wars material so everything produced was funneled into the pages of the regular comic. That left the annuals reprinting strips that had already been reprinted. Presumably, the crossover readership was deemed small enough (or undemanding enough) that this wasn't deemed a problem. The annuals did, at least, publish the strips in colour (at least from the 1980 edition... the first to boast cover-to-cover colour interiors), something the regular British comic didn't do until the 1983 reboot.
The only annual to boast previously-unseen-in-the-UK material was, ironically, that very last one. The animated denizens of Endor shared the pages with a reprint of the third US annual (just a double-length comic, published over the summer to catch the eye of vacationing kids). That strip (The Apprentice) didn't get serialized until after the demise of ROTJ weekly when it became the last SW strip Marvel published in the UK... in the back pages of SPIDER-MAN AND ZOIDS.
The 1980 and 1983 editions, predictably, also included movie adaptations.