It's an advert for a (red or green) Lightsaber toy. Or is it?
Closer examination reveals that this is - despite the prominent placement of the STAR WARS brand (albeit not the official logo.. although several were doing the rounds during the early days of the saga so its perhaps no surprise) and the almost-accuate key art, this is an unlicensed product.
The toy is a "Force Beam", presumably relying on the fact that the official name hadn't yet entered the public consciousness. And there's no attribution of copyright to Lucas or 20th Century Fox.
But, the greatest deception of all is that this back-page advert ran in Marvel UK's officially sanctioned (and - presumably - checked and approved by Fox's UK operation) STAR WARS WEEKLY.
First sighted in issue 11, this Loydale Ltd (of Wokingham). advertisement became a regular fixture over the next few months. Presumably, the penny finally dropped with Fox or Marvel or Palitoy (who held the UK toy license) spotted what was going on and complained.