Several years ago (mid/late 80's) in Telford (about 40 miles northwest of Birmingham- and a strange, fortean place in its own right- birthplace of the industrial revolution; more roundabouts per square kilometre than anywhere else in europe, possibly the world; etc... - There is a point to all of this, bear with me) the indoor junior tennis championships were held at a place called 'The Racquet Centre' (now renamed and restyled into something like the 'Telford International Centre' -no honestly there is a point, keep reading).
Anyway they hired some very large lights called 'Skyscans' which consisted of a large spotlight with a mirror assembly. These Skyscans projected a large number of colour changing lights into the sky that whizzed around in rapid geometric patterns (large circles, stars, explosions from a point, squares, triangles- you get the idea).
The problem was they didn't inform anybody they were doing this. Quite a UFO flap developed as very few people knew of the event, also the Skyscans were quite new at the time, so the lights in the sky were unusual, especially the patterns and the colours. Some of the older folks said it reminded them of the war, with the sweeping beams.
The local newspaper (The Shopshire Star) carried a number of stories relating to the lights and the "UFO Hoax" as they called it. Always desperate for a story is the shropshire star (quite a laff as they often report such unlikely to be reported things as bicycle thefts and cow tippings, also great forteana coverage as they will print anything to make copy) and so they stretched this out for about a weeks news. I remember a BA pilot had been quite shocked as he had overflown the site on route to Birmingham and quite unlike most UFO investigators 'code of silence' theory would suggest reported it immediately. He described the bank of cloud below him lighting up in "a great catherine wheel" of blue lights, that looked to him like it was rising toward him (of course the size of the circle was just being increased as the lights moved around) .
Since then the centre have always warned the appropriate authorities (including the local police I believe) about the use of these lights.
I'm wondering if these lights (possibly combined with a little freak weather following a thunderstorm, high clouds or a temperature inversion to provide the shortened window of 15 mins you saw it for) couldn't be the source (see I told you there was a point to the rambling above- ok not much of one granted).
I don't know how closely the times of the Raquet Centre hosting the Junior Tennis Championships and your sighting correlate (october 1988?!? feels about right but I really can't remember and unfortunately the archives of the shropshirestar.com site are very poor and as I moved way from shropshire a decade ago I can't exactly pop down and check the records- any other salopians/telfordians recall this?), but what I do know is that they carried on using the lights for conferences and things well into the 90's.