Tax on property in London

Hi, I own a flat in London and at the moment the mortgage is interest only. From the rent the tenants are paying, there is a surplus of about £150 per month. Do I need to declare this to the taxman here?

Yes,

See [broken link removed] You need to calculate the profit and declare it to revenue
See "Example Rent account" in particular

You also need to do a tax return in the UK - you pay your tax there first and then you must check if you have an Irish liability to tax