2007 is the Year of Marriage so a tax return & review of that year will be necessary anyway, after the end of 2007, but before the self-employed deadline of 31/10/08. If you file on ROS< the 2007 return could possibly be filed as early as end January 2008, assuming all 2007 data is available, including your spouses self-employed accounts.
The YoM review basically runs along the lines that if the tax paid by you individually in the post-marriage period, exceeds the tax payable by you in that period as a married couple, then the excess is refunded in proprotion to the tax paid by each of you.