Just a quick update - it's the least I can do after all the help I've had.
Had a wasted trip to my local SportsDirect store today - they didn't have any of the items I'd looked up and/or been pointed to on their website
Must confess I'm running out of time (and enthusiasm, if I'm honest). So far I've spent about £70 (of money I didn't really have) on additional gear for this one trip and need to spend even more if I'm to go. Need to go and investigate how much SD charge for their 24hr delivery service, but I have to confess my desire for this trip is around 60% of what it was.
[Edit] Just spent another £30 of money I can't really spare on three items from amazon (insulated foil roll mat, self-inflating sleeping mat and a waterproof trappers hat).
Will they arrive in time? Probably not.