If you house or apartment is on the market for sale or to let, you must have a BER Certificate
Good news from the budget is that
1. First time buyers purchasing a property in 2012 will get 25% mortgage interest relief (for the first two years, reducing after that)
2. Those who bought between 2004 and 2008 are at last getting some respite, their mortgage interest relief will rise to 30%. This should be allowed 'at source' by your lending institution. See Dept of Finance note here.... DoFi MIR