Pheo wrote
Messy, but just hammer a screwdriver all the way through, then turn. Job done.
DUB BOY appears to own a Mk1 Golf, so what he's asking on here for I have no idea.
ANYway, as Viking says, the TDI engines use a paper filter element inside a fixed housing with a plastic cap. Hammer a screwdriver through that and it's expensive. And it won't
help you get the cap off in any case.
The cup wrench tools that fit the filter cap on the TDI also fit the flats on the metal can-type replaceable filters you find on other engines, so it isn't a bad investment. I'd only ever use a screwdriver as a last resort, as it's irreversible - if the filter doesn't come off you can't drive the car. Also, some cars have a feed tube attached to the filter mount that goes down inside the filter can. Hammering a screwdriver through the filter is liable to damage them.