Prime Minister Theresa May has insisted the government is taking air quality seriously and it is planning to bring more proposals forward.

She was probed on the issued by London MP Ruth Cadbury after high levels of pollution which have been seen in the capital in recent weeks, but also in Norwich city centre.

She spoke out after a United Nations expert warned air pollution, which plagues the UK, threatens the human rights of children.

Baskut Tuncak, the special rapporteur on hazardous substances and wastes, said there was an urgent need for the government to protect children and other at-risk groups from the air pollution 'crisis' which causes serious health problems.

Transport secretary Chris Grayling signalled the start of a government war on the use of diesel vehicles in an interview with the Eastern Daily Press and Norwich Evening News this week.

Last week the government issued an air quality warning in Norwich after a local monitoring site recorded the highest level on the PM 2.5 particles index – the measurement of small particles which are created in car exhausts.

In Cornwall people could be moved from their homes to protect them from air pollution, under plans being considered by the council.

Mrs May said today that the issue of air quality was one the government was 'taking seriously'.

She said that £2bn had been committed since 2011 to help bus operators, bin lorries and fire engines to be upgraded so they are less polluting. 'We do recognise that more needs to be done. We have seen an reduction in nitrous oxide from 17pc in recent years but we will be bringing forward proposals to maintain the air quality,' she added.

The Government has repeatedly been taken to court over its failure to meet EU standards on air pollution and has admitted it might not meet the rules in London and some other cities until 2025, well after Brexit.

'I encourage the UK government to fulfil its human rights obligations on air pollution, protecting the rights of children, women of reproductive age, the elderly and those of poor health who are especially vulnerable to toxic chemicals in developing a new plan to tackle its air pollution crisis,' Mr Tuncak said.

A Government spokesman said: 'We have been very clear we are committed to safeguarding and improving the UK's long history of environmental protection, and securing the best deal for Britain as we leave the EU.'

He also said the UK would remain subject to international environmental protection conventions, independent of EU membership.