Lizardking, The OP was asking about mortgage interest supplement. Which is a means tested welfare payment!
Yet you've referred him to a link for mortgage interest relief which is a revenue scheme and has no bearing on his question.
With regards to the OP's query as long as you meet the means test requirements for this benefit, you will receive the payment calulated against the interest portion of your mortgage.
All the information is on this link
http://www.citizensinformation.ie/c...-welfare-schemes/mortgage_interest_supplement