Rather than hammer a screwdriver through the old filter (a practice I detest and one that I have never actually used anyway!), I turned up this correctly sized remover on Fleabay:

http://www.ebay.co.uk/itm/180610505741

Uses 3/8 drive or 21mm spanner and fits the filter perfectly:

I use this:

Got a tub myself. On a shelf next to buckets of steam, boxes of glass nails, tins of Tartan paint and a bag of Tads lol.

Don't forget the rubber rivets to go with the rubber mallet. And don't forget the long weight which is in the stores.

Is it universal fitting or just for Purflux?

Any 76m 12 flute oil filter I would imagine, not necessarily Purflux.

Which is great, until you need to remove one that's a different size or has different flutes.

I like the chain or strap wrenchs, if you've got decent end access - or, if side access is possible, filter pliers really are the dog's...

I bought an old 2cv purflux made oil filter ring tool off ebay ,luck would have it it also fits BX and Xantia filters
Needed to be a bit of a contortionist on the Xantia though

Which ever method you use it's only hand tight on fitting, I recall some idiots on BMW bikes used the fluted tool to do them up aarrghh! Also the original filter for the early 'K' flying brick had a nut welded on to assist removal. This was discontinued after being used to tighten the filters up by some workshops.

Banjo is absolutelly right.
By no means do not tight any ,2cv, Xantia, Bx, etc by any tool!
Only hand tight after applying some oil to the rubber gasket.