Shares in Costain jumped after the construction and engineering group announced that it had reduced its pension deficit by £22m after transferring its interest in six PFI investments into its pension scheme.It said the valuation realised on the investments was higher than expected. As a result of the transaction, an accounting profit of £10.5m will be realised from the investments, Costain said, adding that it expected pre-tax profits for the year to increase by £7.5m.Trading has been strong since the company's last update in August, it said.'Whilst challenging market conditions are set to continue for the foreseeable future, the board expects to report continued progress at the year-end in line with its expectations,' the company said.