Overpayments of tax credits

I note the written parliamentary answer today where the biggest overpayment being clawed back is recovery of tax credits. But my understanding is that only this year’s overpaid tax credits can be recovered (CPAG 18/19 page 1210 )  Have I misunderstood this?  Does it mean that if you are claiming tax credits, and have a deduction for previous years’ overpayments, and then you move for whatever reason to UC, these deductions for, say 2017 to 2018. can carry on, or does it mean that only overpayments for 2018 to 2019 can be recovered?  Ruth

See here: https://www.rightsnet.org.uk/forums/viewthread/14041/#67376

thanks Charles. I briefly thought I had found a loophole for my client.