I have just seen an article in the CPAG Welfare Rights Bullitin on this subject which could be rather problematic. Apparently in SI 2005 NO.828 two people of the same sex counting as a couple will count as achange in circumstances, which could lead to recoverable overpayments.
This means that when the Civil Partnership Act comes into force couples in same sex relationships may need to report them to the Inland Revenue to avoid an overpayment