Basically you pay income tax on the PROFIT you make from the rental - i.e. the rental income less the expenses of running / maintaining the property. Income was 20% the last time I looked, until one earns enough to be a higher rate taxpayer.
i had to write to my local tax office telling them when the rental started and the amount you get. they wrote back saying they would send me a tax return in due course. then they'll work out what i owe them and ill have to pay it.