Clifford Chance has the largest pension liability in the U.K. top 50 and is one of just nine other firms with such deficits, according to research by Legal Week and Smith & Williamson.

CC had a defined benefit pension scheme liability of £283 million by the end of the financial year 2017-18, a 17% improvement on the previous year when it had a liability of £341 million, according to information in its LLP accounts.

In its filings, the Magic Circle firm wrote that it was aiming to eliminate its deficit by May 2026. It added that actuaries had estimated that employer contributions set to be paid to the pension scheme by April 2019 were £18 million, after which contributions will increase year on year in line with retail price index inflation levels.

The statement continued: "Funding levels are monitored on an annual basis and the next triennial valuation is due to be completed as at 30 April 2019. The weighted average duration of the defined benefit obligation is around 26 years."

CC's liability dwarves those of the other nine firms in the top 50 with liabilities. Simmons & Simmons had the next largest liability with £19.6 million, an 18% improvement on 2016-17.

The other firms in the top 10 to have a liability at the end of financial year 2017-18 were Hogan Lovells International (£15.3 million), Norton Rose Fulbright (£8.4 million), Stephenson Harwood (£3 million), Trowers & Hamlins (£2.8 million), DAC Beachcroft (£2.2 million), Withers (£1.8 million), Blake Morgan (£1 million) and Clyde & Co (£900,000).

A spokesperson for DAC Beachcroft said in a statement that its liability arose from a defined benefit pension scheme operated by legacy firm Davies Arnold Cooper, which Beachcroft merged with in 2011, adding that the scheme is now in run-off.

The statement continued: "The firm has an approved plan in place to address the current deficit and will continue to meet the running costs of the scheme during the run-off period. The firm now operates a defined contribution pension scheme."