Sky News understands polling station staff were forced to send the former prime minister away after he initially failed to comply with legislation he introduced while he was in Downing Street.

Mr Johnson, who introduced the Elections Act requiring photo ID in 2022, was attempting to cast his ballot in South Oxfordshire, where a police and crime commissioner for the Thames Valley was being selected.

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He posted on X on Thursday morning: "The polls are now open. Vote Conservative today!"

The Elections Act has proved controversial, with fears that it would prove a deterrent to voting, particularly among disadvantaged groups.

In 2023, the Electoral Commission warned the new law, which requires people to show acceptable forms of photo ID when voting in person, could exclude hundreds of thousands of people, including those with disabilities and from minority ethnic backgrounds.

The commission found that in local elections last May, 14,000 people were not able to vote because they did not have acceptable ID.

In England, passports, driving licences, blue badges and certain local travel cards are accepted forms of voter ID.

A spokesman for Mr Johnson did not deny he had failed to bring ID, saying only: "Mr Johnson voted Conservative."

Meanwhile, the government has also said it plans to make veterans' ID cards a valid form of voter identification after former service personnel were turned away from polling stations.

Veterans minister Johnny Mercer apologised to those who had been unable to use their veterans' ID card to vote in the local elections, vowing to "do all I can" to have it added to the list of valid identification.

A Number 10 spokeswoman said: "It is our intention for the new Veteran Card, which was rolled out in January, to be added to the official list."

Mr Mercer's apology came after Army veteran Adam Diver complained he had been turned away from his local polling station after presenting his Veteran Card.

Mr Diver, 48, had been looking to place his vote in Fleetwood, Lancashire, but was turned away after presenting his card, and described the experience as leaving him feeling "gutted".

Labour said the government has had years to ensure the Veteran Card was included on the list of valid voter ID, having begun rolling out the cards in 2019.