No one in Italy understands the difference between Scotland and England - "English" is the shorthand for everyone in the UK. The Ministry of Health circular referred to paperwork provided by the UK, so as long as Scotland doesn't secede between now and September you should be fine. If they ask you just say it's the British certificate, or the UK certificate, of if that fails hold your nose and say "E' il certificato inglese" and that'll do the trick.