Pension fund deficits of one in ten of the UK's top 350 companies is equal to 20% or more of their stock market capitalisation and five of the 100 largest firms have deficits so large they are equal to 29% or more of their market capitalisation, according to Mercer Human Resource Consulting.

Overall, deficits in the UK's top 350 companies fell by just £10bn ($18bn) last year despite the stock market rally, according to Mercer's analysis.