Boris Johnson has been warned that his plan to guarantee full fibre broadband across the UK by 2025 may not be possible without ”100 per cent commitment” from the government.

The telecoms industry has published an open letter urging the new prime minister to take immediate action within 12 months to ensure the target is met.

It sets out four key issues which need to be resolved, including reforms to building regulations and the tax on fibre cables, prioritising investment in digital and engineering skills, and allowing telecommunications providers access to properties when landlords are “unresponsive”.

“Nationwide full fibre coverage is not a can that can be kicked down the road, and these issues need to be resolved by your government within the next 12 months to ensure that industry can continue to accelerate rollout,” the letter concludes.

“Industry is ready and willing to work with yourself, your government and the new digital secretary to ensure that Britain’s connectivity is fit for the future. But that work needs to start now, and 100 per cent fibre coverage requires a 100 per cent commitment from government.”

The letter is signed by the chairman of the Internet Services Providers Association, the interim chief executive of the Federation of Communication Services and the chief executive of the Independent Networks Co-operative Association, whose members include BT, Sky, Virgin Media, Google and Vodafone.

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During the Tory leadership contest, Mr Johnson said the existing government target of universal broadband by 2033, announced by former chancellor Philip Hammond in May last year, was “laughably unambitious”.

He pledged to deliver it within the next five years instead, despite some projections suggesting that the target of extending full fibre to 30 million homes would not be met until 2043.

The National Infrastructure Commission has estimated that building and maintaining a full fibre network across the UK would cost £33.4 billion - most of which would come from private investment.

In its open letter, the industry said the pledge was “ambitious” and “requires a mix of leadership, pioneering spirit and government support to be possible.”

“We need a prime minister who can provide the direction, idealism and commitment to fulfil this ambition,” the sector writes. “We call on you to give a full commitment that your government will give us the tools we need to deliver future-proof connections across the UK.

“Ambition alone is not enough to overcome the scale of the considerable task ahead.”

A spokesman for the Department of Digital, Culture, Media and Sport said the government was “committed to creating the right opportunities for investment and speeding up the rollout of the required digital infrastructure.”