The Government will bring forward new policies to reduce air pollution following a High Court ruling that it is not doing enough, Theresa May has signalled.

At Prime Minister’s Questions on Wednesday the PM accepted the ruling that the Government had failed to take steps to bring the UK into compliance with the law “as soon as possible”.

She said there was “more to do” on the issue and said the Government would take action to bring policy in line with the law.

“I have always made it clear that we recognise that there is more for the Government to do,” the Prime Minister said.

“We have been doing a lot in this area. We have been putting extra money into actions that will relieve the issues around air quality, but we recognise that the Department for Environment, Food and Rural Affairs now has to look at the judgment that has been made by the courts, and we have to look again at the proposals that we will bring forward.

“Nobody in this House doubts the importance of the issue of air quality. We have taken action, but there is more to do and we will do it.”

The PM’s statement comes after ClientEarth, the NGO which took the Government to court over the issue, said Ms May had to “take personal control” of the “urgent public health crisis”.

Opposition politicians however criticised the PM’s record. Liberal Democrat leader Tim Farron said some of the Government’s flagship policies were incompatible with bringing air pollution down to legal and safe levels.

A seagull flies above the smog-filled skyline of the City of London (Reuters)

“This ruling deals a huge blow to the Theresa May's reckless Heathrow expansion plans,” Mr Farron said.

“The Government has already illegally delayed meeting EU pollution limits until 2025, building a third runway would make the situation even worse.

"Without sensible EU safeguards, this Conservative Brexit government will be free to disregard targets which are there to save lives and improve people's health.

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"The Liberal Democrats will fight against Heathrow expansion and to ensure vital EU air quality limits are not scrapped.”

The British Lung Foundation also welcomed the ruling. Dr Penny Woods, the group’s chief executive, called for “further and faster action” on the issue.

“It’s a public health crisis. That’s why we urgently need a new clean air act that restricts the most polluting vehicles from our urban areas and protects everyone’s lung health,” she said.

The judge in the case, Mr Justice Garnham, ruled that the Government had used an overly optimistic model of pollution when deciding on its policies.

“It seems to me plain that by the time the plan was introduced the assumption underlying the Secretary of State's assessment of the extent of likely future non-compliance [with legal pollution limits] had already been shown to be markedly optimistic,” the judgment said.

In a statement issued after the judgment, a spokesperson for Defra said: “Improving air quality is a priority for this Government and we are determined to cut harmful emissions.

“Our plans have always followed the best available evidence – we have always been clear that we are ready to update them if necessary and have been at the forefront of action in Europe to secure more accurate, real-world emissions testing for diesel cars.

“Whilst our huge investment in green transport initiatives and plans to introduce Clean Air Zones around the country will help tackle this problem, we accept the court’s judgment.