More than half a million British children are unvaccinated against measles, new figures show, as the head of NHS England challenged social media giants to block “grossly irresponsible” anti-vax propaganda.

Sites such as Instagram and YouTube should adopt “zero tolerance” regimes, Simon Stevens said as Unicef data revealed the UK to be among the worst high-income countries for uptake of the jab.

The new data, which tallies children left unvaccinated between 2010 and 2017, follows a steep rise in measles cases in England last year.

The hike is thought to be a direct result of the drop in vaccinations that followed the publication of fraudulent research linking the Measles Mumps and Rubella (MMR) jab to autism by the disgraced British doctor Andrew Wakefield in 1998.

Vaccination coverage among children reaching their second birthday in England is now 91 per cent, with just 87 per cent receiving the second dose by their fifth birthday.

This falls below the 95 per cent coverage experts believe is necessary to achieve “herd-immunity”, where outbreaks are effectively unable to spread.