The telecoms firm taking over Glasgow rival Thus has offloaded £1 billion of pension liabilities under a deal with Prudential.

Cable has bought a bulk annuity policy which will see Prudential assume responsibility for benefits payable to the firm's 5,000 pension-plan members.

The annuity reduces the Cable pension fund's exposure to liabilities by 50%. The firm said the benefits of the fund's members, including active employees and deferred pensions, were unchanged by the move.

Finance director Tony Rice added: "The transaction materially reduces the fund's exposure to liabilities by over £1 billion.

"It also materially reduces the fund's and shareholders' exposure to the future risk of adverse changes in actuarial assumptions and investment returns."

Cable shares were 2% higher following today's announcement.

Investec analyst Jonathan Groocock said the de-risking of the pension scheme represented another step towards a "value realisation" event for shareholders, such as the demerger of the UK and international operations.

"There is the possibility that further details of such an event may come at the interim results on November 10," he added.

With Prudential assuming responsibility for the benefits payable to the UK fund's 5,000 pensioners, the deal leaves 9,000 deferred and 1,000 active members.

Mr Groocock added: "Management has previously said that the cost of fully offloading the pension scheme is unattractive. Given the longer duration of the deferred and active member liabilities, there is significantly greater risk which makes it harder to offload that side of the UK pension scheme."

Today's agreement is the largest of its kind in the UK this year and means more than £7.5 billion of bulk annuity business has been written in 11 months.

Watson Wyatt, the lead adviser on the transaction, said it expected more transactions on the scale of the Cable agreement.

Steven Dicker, a senior consultant at Watson Wyatt, added: "This is a landmark deal which delivers significant risk reduction for both fund members and Cable & Wireless."