In our post on why buy-to-let incomes are dropping, we saw how the staged removal of mortgage interest relief has led to landlords paying more tax.
The example we quoted in that post was of a higher-rate taxpaying landlord who each month receives £1,150 in rent and pays £700 in mortgage interest payments. Before 2017, they would have had a tax bill of £2,160 leaving them a post-tax rental income of £3,240. From April 2020, an increase in tax to £3,840 would leave them with only £1,560 after tax.
Depending on your circumstances, you may be able to cut your tax bill significantly if you are married.