Downing Street has denied Theresa May dodged reporters at an EU summit to avoid questions about the National Insurance hikes controversy.

The Prime Minister was running late when she arrived in Brussels and wanted to “crack on with work”, her spokesman said.

Meanwhile, No.10 was also forced to insist she had full confidence in a Government minister who said there was a need to “apologise” to voters over the row.

Ms May raised eyebrows in Brussels when she skipped the usual red carpet entrance for EU leaders which would have allowed her to be questioned, entering the venue by a different door.

Asked to explain why, her spokesman said: “She was running a bit late and thought the most important thing to do was get into the building and crack on with work.”

It came after No.10 refused four times to rule out a review of the controversial increases in NI for self-employed workers, raising suspicions of a retreat.

The spokesman pointedly refused to rule out re-opening the Budget, just one day after it was delivered – after up to 18 Conservative MPs demanded an urgent rethink.

Ms May is due to face reporters at a press conference this evening, after holding talks with fellow leaders on migration and economic growth.

The Budget announcement will see the nine per cent rate of Class 4 NI contributions go up to ten per cent in April 2018 and to 11 per cent a year later.

According to the Treasury, 1.6m self-employed people will pay £240 on average more every year – but no-one earning less than £16,200 will be worse off.

Embarrassingly for ministers, the 2015 Conservative manifesto explicitly ruled out rises in National Insurance, VAT and income tax during the lifetime of the current Parliament.

That embarrassment grew when Guto Bebb, a Government whip as well as a minister in the Wales Office, told the Welsh-language BBC Radio Cymru: "I believe we should apologise.

“I will apologise to every voter in Wales that read the Conservative manifesto in the 2015 election.”

Asked whether Mr Bebb could face the sack over his comment, the spokesman said: “We have heard a number of opinions expressed today.