The UK government has quietly revealed a loophole which may allow dual British-Australian citizens to travel back home on an expired UK passport.

From tomorrow, the UK's Electronic Travel Authorisation (ETA) scheme will be fully enforced following a long grace period – meaning travellers from dozens of countries, including Australia, need to pay £16 ($32) for a visa waiver.

British and Irish citizens, however, won't need to apply for an ETA to visit.

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