The government is “looking very seriously” at making vaccinations compulsory for state school pupils and has taken advice on how such a law could work, the health secretary has said.

Matt Hancock, a vehement critic of anti-vaccination campaigners, has previously suggested such a plan. Speaking at a fringe event at the Conservative party conference, he said he was “very worried” by falling vaccination rates, indicating the government could act soon.

“I’ve said before that we should be open-minded, and frankly, what I’d say is that when the state provides services to people then it’s a two-way street – you’ve got to take your responsibilities, too,” Hancock told the Q&A session hosted by the Huffington Post.

“So I think there’s a very strong argument for having compulsory vaccinations for children when they go to school, because otherwise they’re putting other children at risk.

“Then I’d want to make it very easy if the children do arrive at school not vaccinated, simply to get vaccinated, and make it the norm. But I think there’s a very strong argument for movement to compulsory vaccination, and I think the public would back us.”

Several US states, including California, have introduced such laws for state school pupils but also faced lengthy legal challenges.

Asked about such potential opposition in the UK, Hancock said: “Actually, I’ve received advice inside government this week on how we might go about it, and I’m looking very seriously at it.”

The UK has lost its official measles-free country status from the World Health Organization after a gradual fall in rates of MMR (measles, mumps and rubella) immunisation.

Figures released earlier this week showed that for vaccinations administered at the ages of 12 months, 24 months and five years, there has been a marked decline for 13 different diseases, including whooping cough, diphtheria and meningitis.

Hancock said this was “a serious problem” and added: “It’s unbelievable, I think, that Britain has lost its measles-free status, and it should be a real wake-up call. I think that the social media companies have got a lot to answer for, because they allow the spread of anti-vaccine messages.

“I will do whatever I can – the science is absolutely clear and settled on the importance of vaccination. And the worst thing is that if you don’t vaccinate your child, and you can, then the person you’re putting at risk is not only your child but it’s also the child who can’t be vaccinated for medical reasons.”

Hancock said that vaccination rates below 95% lost the so-called herd immunity effect, and thus put at risk children unable to be vaccinated, for example those undergoing treatment for cancer.

He added: “You’ve got to make sure the system would work, because some children can’t be vaccinated and some may hold very strong religious convictions that you’d want to take into account, but frankly, the proportion of people in either of these categories is tiny, compared to the 7% or 8% now who don’t get vaccinated.”

Hancock first raised the idea of compulsory vaccinations in May, saying he did not wish to do it but might be forced to act if no other solutions to improve take-up rates could be found.

He said: “Those who have promoted the anti-vaccination myth are morally reprehensible, deeply irresponsible and have blood on their hands.”

Confidence in the MMR vaccination seems to have dropped at least partly in response to social media misinformation and scare stories. The discredited claims of Andrew Wakefield, who in 1998 theorised that the jab was linked to autism, are widely circulated.

Wakefield was struck off the medical register in 2010 after suggesting a link between the MMR vaccine and autism.