Ask for Registration documents with the UK kennel club, are they a registered breeder if so ask to see the MoM and Dad , references from other purchasers , ask for there Vets phone number and call them about the pup . I am sorry I use only reputable breeders, I do not buy from Kijiji, Craigslist list and or similar sites pet stores ect ect you have no idea where the pup has come from . Here in Ontario Canada , Old English Bulldog pups start at app $2500.oo Canadian dollars not sure what that equals in EU or pounds but it is a lot , so if it sounds to good to be true it could be . Contact a real reputable breeder ask what they sell there pups for to give your self a idea of cost , also keep in mind these dogs can be expensive in vet bills , some never have issues some do like anything else .
Spend some time on the site here read all the advice you can find if you have a question ask , everyone here loves the breed and will help, some have multiple Bulldogs . there are tons of pics of bulldogs here lol were anal that way we love pics, look thru them see what ya think M8