Professor Mike Kelly, director of the Centre for Public Health Excellence at NICE, said the concept of nudging was not new but had been shown to work in other settings.

The tactic involves encouraging people to be healthier through positive advice without restricting choice through legislation.

Evidence for health-related nudging is ‘limited but improving’, Professor Kelly told attendees at the UK Faculty of Public Health annual conference in Birmingham on Monday.

But Professor Kelly warned: ‘I think there is still the question of what the unintended consequences of the nudge approach might be, not least the ethics of keeping people aware of what [public health] is doing.’

He said any nudge tactics must be specific about the behaviour they are attempting to change. The complex interaction with other aspects of behaviour must be considered too.

‘It isn’t good enough to talk about behaviour change in general – you have to be specific about what you are trying to do,’ he said.

‘The operation problem of only thinking of nudge in a small way is where the causal relation between the nudge and the outcome is distal, where some sort of lengthy process is at work. Does nudge still work then?’ he said.

‘We are by definition dealing with complex definitions, settings and behaviours, necessarily easily amenable to bite size ways of describing the problem.’

The BMA has been vocal in its dissent of the policy.

In February, Cambridge University researchers argued that, while nudging can alter behaviour, it often moves people towards unhealthy choices.

There is little evidence to support the effectiveness of nudging improving population health and reduce health inequalities, they said.