retrospective tax rebates for married couple

Hi,

looking some advice please, myself and my wife have been married for nearly 7 and half years now, but have never actually ever fill in a the relevant revenue form to register for joint assessment.

I have just discovered that last year 2011, my wife didnt use all tax credit at the 20% tax rate. This may have been the same for some other previous years too.

So I wondering if we register for joint assessment now, is there any way that I can claim to use unused tax rate of 20% and get a rebate on the tax i paid at 41% for last year and what about years further back from last year?

Appreciate any advice or knowledge anyone may have on this.
thanks

You can go back 4 years only, fill in returns from 2008 onwards.

Thanks wbbs,

so is it possible to transfer the unused proportion of my wifes income rate taxed at 20% across to a proportion of my income charged at 41%? and can this be claimed for teh 4 previous years?