Adopted in Canada by British parents in 1967

Hi, my husband was born in 1966 in Canada and adopted by British born parents (British citizens) in 1967. The family moved to the UK in 1968.
The family then moved to and from Australia a few times and he has now settled in the U.K.
When the family moved to the U.K. in 1968 they used his adoption papers to bring him into the U.K.
His mother then added him to her passport for future travel? Does the fact that he travelled on his mother’s passport have any relationship to his citzenship?

How can we find out whether his parents registered him in the UK when he was originally brought to the U.K?
Whilst living in Australia he wanted to obtain a passport and was advised that he must apply for a Canadian passport and then apply for a ROA to live in the U.K.
Does he qualify for British Citizen ship?
Can he apply for a British Passport?
What is his immigration status if his ROA is in an expired passport?
When his adoption was registered in Canada his certificate states that he has the same immigration rights as his parents? Does this mean anything in U.K. law?
Does this mean that if he had remained in Canada he could have applied for a British Passport?

Thank you, really hope you can help

Does your husband already have Right of Abode in an existing (even if not current) non-British passport? Does it have any indication on it about when the RoA was issued?

Hi, he has a ROA already issued in 30th June 1994.
We travel regularly and immigration accept his ROA in his old passport accompanied by his valid Canadian passport.
He has been applying for a new role and the company wants to offer him but cannot accept his ROA in his old passport.
I am trying to establish what exactly is a ROA?
Is it the right to work and stay indefinitely in the U.K.? If it is, how can it expire?

Right of Abode means what it says- your husband has the right to live, work, study etc. in the United Kingdom with all the rights of a British citizen except a British passport. Also the right to vote. He has this as a Commonwealth country (Canadian) citizen adopted by British born parents before 1983. It cannot be lost as long as he remains a Canadian citizen, although in recent years the Government has tightened up on the evidence requirements to prove Right of Abode. He will need a new stamp in order to use his status.
https://www.gov.uk/right-of-abode

IF he was added to his mother's British passport, it should mean he was registered as British (only British nationals should be included on British passports)- although not necessarily. The procedures for adding children to British passports in the past were not as strict as they are today.

If he was registered as a Citizen of the U.K. and Colonies as a child, this could have been done at either the British High Commission in Ottawa (or Canberra) or at the Home Office, if it was done after returning to the U.K. Pre-1986 Home Office records may be available from the National Archives.
https://www.gov.uk/get-replacement-citi ... ertificate

If he was registered at one of the High Commissions- there is no information available as to what happened to the pre-1983 citizenship records. You may be able to gain some further details by writing to the Foreign Office in London.

And if there is no record of him being granted British citizenship- then he may apply for naturalisation as a British citizen, if he meets the normal residence requirements.
https://www.gov.uk/becoming-a-british-citizen