More than half of all private medical plans offered to employees through their companies discriminate against unmarried couples, according to a survey by consultants William M Mercer.

Only 48% of the 527 plans surveyed allowed membership by common-law spouses, with 44% giving cover to same-sex partners.

“Surprisingly, a significant number of plans appear to be out of tune with social trends,” said European partner at William M Mercer, Steve Clements.

“As things stand, many employers could be accused of acting unjustly, as a large proportion of partners are not allowed membership.”

But he said the signs indicated that companies were increasingly looking to address the issue.

Stress-related illnesses were a com-mon exclusion – one in eight plans did not cover employees for such conditions.

A quarter of full-time workers and almost half of part-timers declined to take up the offer of company health plans. Reasons for this included tax implications and duplication of healthcare benefits between spouses.

Half the companies surveyed paid for their employees' health insurance, but not for the employee's family. Only 46% of schemes paid for full family cover, with 3% covering employees and their spouses.

Four in ten of the firms surveyed offer private medical insurance to all employees. The average cost of membership was £314 for individual and £691 for family membership.

“The trend in recent years has been to extend private healthcare down the organisation,” said Clements. “At one time, it was restricted to senior management; today, it is offered much more generally throughout the company.”