The firm, which yesterday released its interim results, reported up until 30 June this year the scheme's deficit stood at £75.7 million - an increase of £39.6 million since December 2008.
In the company's interim statement, David Allvey, chairman, and Andrew Wyllie, chief executive, wrote: "As part of our plan to manage the pension obligations and reduce volatility, we are approaching the end of a consultation process with staff regarding a proposal to close the defined-benefit pension scheme to future accrual.
"The proposal to close the scheme follows the increasingly disproportionate risks and costs arising from a combination of factors including rising life expectancy, interest rate volatility and lower investment returns."
The firm closed the defined-benefit scheme to new members in 2005.
