To find this micro cache, you'll need to own, see, find or otherwise have information from an Aluminium Alpha Numeric Disc (aka AAND), the colour of which there is a clue to on this page. The cache is at the end of a trail of reflective markers which begin at N51° 4H.JFK W 000° 5C.KJJ.
Alternative finding method, as required by Groundspeak:
(This is a lot less fun than tracking down one of the hundreds of this colour item released into UK caches and at events in the summer of 2012, but as a last resort..!)
C is nothing important.
F is Night
H is the second Is
J is Silent
K is the second All
(Remember, no two letters give the same number!)
From a location with a guitar connection, follow the reflective markers (you'll need a good torch) and basically go straight on unless there's a marker at a junction to show you the way. If you overshoot a marker and can't see another, backtrack. If you then see a marker clearly hidden from the previous one, it's because you've overshot a turn or junction. When you have several at the same spot, that's where the cache is. Good luck!