Plaid Cymru and the SNP have always argued that their joint parliamentary group at Westminster helps them punch above their weight.
So when Plaid called for Tony Blair to be impeached, the SNP piled in, and when the SNP reported the Blair Government to the police for allegedly selling peerages Plaid wrote to Plod too.
But the Celtic alliance does not appear to be working on today's big issue - MPs' expenses.
The SNP were swiftly out of the blocks, promising to publish their letters from Sir Thomas Legg and challenging other parties to do the same. "There should be complete openness and transparency," said the SNP MP John Mason.
Plaid were rather more cautious, their three MPs spending several hours discussing what to do. Eventually, a statement arrived summarising their Legg letters.
Apparently Sir Thomas has asked them to provide more information on mortgage payments. There have also been individual requests about claims for "maintenance work, council tax and water rates, ground rent, buildings insurance and the purchase of an item of white goods."
Many MPs across all parties have received similar letters asking for information. Sir Thomas has not as yet advised any Plaid MP to repay any money, although they will if he does.
But will they, in the interests of "complete openness and transparency" rise to the challenge set by their Westminster group partners?
They're going to get back to me on that one.