Passport for child issue

[EuromumAussiekid]

Just wondering if anybody can answer this question for me

We live in Britain and ds has both an EU and Australian passports.

Later this year we plan on visiting family in the EU. Ds eu passport has expired ( but not cancelled, so it is still a legal form of ID) and I am a bit broke and want to avoid replacing it at the moment.
So if we travel with the in date Australian passport and also the expired ( not cancelled) eu passport will that be enough to get us back into the uk ?

I'd ask the passport office. I've always found them helpful

Why can't he travel out and back on the Aus passport? Do you need visas?

He needs a valid EU passport to return to the UK because the Australian visa waiver scheme is only for visits, not permanent residence.

Doesn't he need a visa then to go to the Eur country you're visiting?