Fingers crossed your mate is reunited with their passport. If not, here's a link on how to apply for an emergency travel document
https://www.gov.uk/travel-urgently-from-abroad-without-uk-passport/how-to-apply
*EDIT* Added a link from ABTA on advice on steps to take if you lose your passport...
Will take a bit of time between Scotland gaining independence and applying to re-join the EU and being accepted into same. Having a Scottish passport will be pretty neat tho 🙂