Different freewheels and cassettes require specific removers.
After a bit of digging around, it seems the one you need is quite scarce (unless you were to go to France, where I imagine they are plentiful).
A Bicycle Research Tools' Normandy/Maillard CT-3
will do the job: they do have a UK distributor (Townsends of Cambridge
), who I called but they referred me to their sister company who deal with the importer (Billy's of Cambridge
) but I drew a blank with them also.
I can only suggest you try your LBS who might have one gathering dust somewhere, local clubs or put a wanted ad on here.
Depending on the age of your Pug, it may have French threads (I believe they adopted British threads over a few years in the eighties) and an obscure size of seat post.