Such an obligation already exists.
Paying parents who are in the Child Maintenance Service must declare changes in income immediately if they vary by more than 25% of the previously declared level. Of course every paying parent is subject to an annual review, where adjustments are made to the payments if required.
My hon. Friend raises an extremely important point. As he may know, we have just finished a consultation on what greater powers we can take to ensure proper and efficient recovery for those in receipt of support. We are looking at a series of measures, not least integrating our information systems much more closely with those of Her Majesty’s Revenue and Customs, so that we have a fuller picture of people’s income. We will be looking at proposals to make estimates of unearned income and, indeed, imputing income from asset values for those who attempt to conceal their income but still hold very significant assets. In the final analysis, we may well take powers, depending on the results of the consultation, to deny people a passport—and remove their passport—if they refuse to pay.