The researchers looked at outcomes for three commercial slimming clubs and three NHS programmes: primary care nurse-led counselling, pharmacy-based counselling and group-based dietetics.

All these groups were compared against a control group who were all given 12 vouchers for free leisure centre use but received no other intervention.

At 12 weeks, all three commercial programmes (Rosemary Conley, Slimming World and Weight Watchers) achieved weight loss beyond that seen in the control group, but none of the NHS programmes did.

At one year, only the Weight Watchers programme was able to achieve weight loss beyond that seen in the control group.

The nurse-led and pharmacy-based counselling did not achieve sustained weight loss at one year.

The researchers calculated that, at around £55 for a 12-session course, commercial programmes provided better value for money than funding NHS programmes.

Professor Paul Aveyard, who led the research, said the findings represented ‘a significant step forward’ in assessing weight-loss services’ relative quality and value.

‘Its conclusions should be of significant interest to commissioners: of all the services we tested from both the NHS and commercial providers, at programme end only the commercial programmes had significantly greater weight loss than those patients who were left to "go it alone".’

A spokesman for Weight Watchers said the results provided ‘a clear message for GP commissioners about how to achieve value for money in commissioning weight management programmes, at a time where they're being asked to deliver more for less with regard to public health outcomes’.

The study’s findings were presented at the European Conference on Obesity last week.