Cgnu will pay an extra $200m (£138m) to White Mountains to cover transaction expenses on the sale of its US general insurance business to the Bermuda-registered insurance group.

CGNU said the sum would cover due diligence, management costs, and shortfalls in the company pension scheme that needed to be settled to achieve regulatory approval for the transaction.

In September 2000, CGNU announced it was getting out of the US property and casualty market with the sale of its US general business to White Mountains for $2.06bn (£1.42bn), plus the repayment of an inter-company loan of $1.10bn (£0.76bn).