The roll-out of an online claims system for Universal Credit in November could have a "Scrooge effect" and leave families penniless at Christmas, former minister Frank Field has claimed.
The Labour MP has written to Work and Pensions Secretary David Gauke to express fears that expanding the operation to 27 more local authority areas at that time of year could add to hardship already caused by delays in payments.
Former social security minister Mr Field said that the roll-out of the online only system could cause "chaos" over the festive period.
He wrote: "Such a revolutionary transition to the full service shortly before Christmas risks leaving large numbers of families without money, and facing misery, over the festive period.
"There is, of course, the six-week wait which new claimants must endure even if their claim for Universal Credit is processed on time.
"It is not inconceivable that a family with children making a new claim in mid-November could be left without money on Christmas Day, even if the system processes their claim as planned.
"Given, though, that the current system struggles in some cases to cope with its existing caseload, the new system being rolled out just before Christmas could trigger all sorts of chaos."
A Department for Work and Pensions spokesman said: "We are rolling out Universal Credit in a gradual, safe and secure way, and already over half a million people across the country are claiming the new benefit.
"Universal Credit is designed to mirror the way many people in work are paid, and budgeting advice and benefit advances are available for anyone who need extra help."