Travelling on non-EU passport as EU passport expired

Hi,

My neighbour has a dual citizenship (EU and non-EU) and holds a PR in the UK (as an EU). His EU passport has just expired and he needs to travel next week within the EU.
Could he travel on his non-EU passport together with his PR document (he is a non visa national) ?
would UK immigration let him in as an EU citizen in spite of the expired passport? And more importantly - would the airline let him board the return flight?
Any advice / thoughts appreciated.

Doesn't he have an i/d card? That would suffice for travel in the EU.

If not, he takes his chances. I don't know why you assume that an airline or border control would acept him for travel to Europe, never mind coming back to the UK. Either way, it's entirely up to the check-in staff and immigration authorities whether they will let him travel, no-one can give you a definitive answer here.

I think all travellers to and from the UK or anywhere else must be in possesion of a valid Identity document. Well said by Mr Rusty.