I can confirm that letting a room in one's home MAY not be taxable.
In 2010/2011 a person could earn up to £4,250 a year tax-free income (or £2,125 if you're letting jointly). This is known as the Rent a Room scheme. That amount remained through 2014/2015 tax year.
The room or rooms must be in a residential premises that is situated in the State and that is occupied by an individual as his/her sole or main residence during the particular tax year. An individual may live in more than one residence but can only avail of rent-a-room relief in respect of his/her sole or main residence.