The government has already made the mistake of abolishing the right to claim interest losses from rental property against other income. The turmoil in the rental market that occurred when investors took flight was so great, that it was reintroduced within two years. I believe the government is unlikely to make the same mistake twice.

But in the unlikely even that it does, I wouldn't expect the change to be retrospective and it would be a matter of adjusting the debt to balance the rental income.