You need an oil filter chain wrench.
This is why i keep telling everyone to buy the K&N oil filter with the nut on the end, it's soooo much easier.
You can always pop down and see any mechanic and ask nicely if they can just loosen it for you enough to break the seal, then undo it properly when you get home, other than that a chain wrench is about £4 delivered on Ebay, or pop out and get one from a car parts shop.
I'm not a fan of the screwdriver trick, 'cos not only can it go horribly wrong, but it's also messy!