Claims that the European ruling on the part-timers' pensions test case will cost British employers many billions of pounds are "simple scaremongering", according to benefits consultancy William M Mercer.
Figures of between £10bn and £17bn have been quoted in the wake of the European Court's decision in Preston and Fletcher v Wolverhampton Borough Council and Midland Bank. It said limiting the backdating of part-timers' entitlement to pension rights to two years was unlawful, opening the way for claims to be dated all the way back to 1976.
But the cost to industry is likely to be closer to £100m, said David Marshland, William M Mercer's employment law specialist. This is because the ECJ has upheld the six-month limit for bringing claims after leaving employment. Also, the House of Lords might yet apply the general limitation period in British contract law of six years.
Further factors are likely to hinder the ability of part-timers to bring claims, Marshland said.
"Probably only a quarter [of Britain's six million part-timers] stay with the same employer for more than two years - the minimum period usually needed to qualify for preserved benefits," Marshland said.
An added complication is that claimants must find an equivalent full-timer of the opposite sex, and many part-timers work in jobs where there are no equivalent full-timers. Claimants must also be prepared to pay their share of back-dated pension contributions.
Other advisers have, however, put the potential cost much higher, partly because the cases have trade union backing which may help claimants meet the cost of their own contributions.
"Also, nearly a quarter of all UK pension schemes are non-contributory, so backdated membership would be free."