Worsening pension liabilities could further complicate the United Biscuits sale, experts have warned.

The Campbell Soup Company emerged this week as the latest player understood to be mulling a possible £1.5bn break-up bid for UB's biscuit-making operations, which include McVitie's Jaffa Cakes and Penguin.

City experts warned UB's pension liabilities and deficit could create further challenges for private equity owners PAI and Blackstone in offloading the business.

Despite reporting £1.26bn in revenue in 2009, UB's pension scheme had assets of £1.24bn and ­liabilities of £1.39bn at 2 January 2010, creating a £153.3m deficit. The net pensions deficit is £111m. At 3 January 2009, the scheme had assets of £1.18bn and liabilities of £1.12bn, giving a surplus of £65.5m, showing the scheme deteriorated by £218.8m over 2009.

"The deficit will stand in the way but it's a question of how people choose to ­react to it and what impact it has on valuations," said one dealmaker.

Shore Capital analyst Clive Black added: "Anything up to two or three times the deficit and two thirds or three quarters of the liabilities may be asked for by the pension trustees to allow a deal."

The move by Campbell appears to be a u-turn as it sold its UK and Irish business operations to Premier Foods in August 2006 for £460m, offloading Oxo, Batchelors, Homepride and Fray Bentos.