CallMeYourMajesty

Hopefully someone can shed some light on this. I've been a landlord the last few years and have always submitted my self assessment tax returns. I was under the impression mortgage interest doesn't count as an allowable expense, but I've done some Googling this week and found out it's possible to claim a tax credit of 20% of the interest element of your mortgage payments. So my questions really are: i. If I haven't started claiming my mortgage interest until now, would that be an issue for HMRC? I'm sure I can get my statement records from the mortgage lender that'll show my interest payments. ii. I'm not really sure how many years back in which I could claim? I'm assuming I would have to go through my old self assessments and input figures and then wait for HMRC to issue the tax credits from the previous years. iii. If I were to take out a remortgage to do some renovation works on the rented property, would the setup fees for the remortgage also be able to be marked as an expense and in return receiving a 20% tax credit? Thank you