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You can get married in the UK once you recieve his Passport and thereafter make an application for leave to remain
The correct way of doing the process is to go back to India and apply as any application made from the UK will be refused as he is an overstayer. If, say for instance you had a child in the UK then he would be able to apply from within the UK
There has to be good reason of why he cannot go back to India to apply
He can do it however there has to be a good reason of why he cannot go back and apply from India otherwise the application will be refused,
They will then be able to argue your case so you'll recieve the best outcome
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