I've been using OS maps for years and find them unparalleled in their accurate depiction of footpaths, bridleways and public rights of way. So to help you find the cache, I've taken a snapshot of the OS Explorer Map and marked it exactly with a big red cross... couldn't be easier, right?
Except that to make sure it wasn't too easy, I've airbrushed out all the identifying text and saved a new version.
In fact I was having so much fun with the graphics editing software, that I started experimenting with flipping the image, vertically and horizontally. Then just for a laugh, I tried rotating it through 90°, then 180°, then 270°, just so it might fit better with the cache page text. Mind you, once I looked at the result I did think that perhaps I'd gone a few steps too far so I tried to put everything the right way round again. Unfortunately I couldn't remember how much I'd done, so undoing it all, was a bit tricky. It might not be quite the right way round that it appears on a real map. Maybe looking at it in a mirror or turning your screen upside down might help... or maybe not...
So... yeah... sorry about that.
I do know that I didn't start stretching any of the sides of the map, so the 'aspect ratio' is still the same, except that after my playing, I can't find the scale thingy. But I don't expect you'll need that... probably...
Anyway, once you think you know where it is, pop your guess in to the geochecker which has been calibrated on the generous side to make it fairer; you only have to get to the nearest 50 metres. You're looking for a 'clip-lock' round plastic container.
I'd appreciate logs not containing any info about which mention caches you may have done before or afterwards - which would rather give the game away, wouldn't it?! Any finders whose logs include such information may be asked to edit them.