DOUGLAS Ross and his Scottish Tories have been urged to “at long last find a backbone” as Boris Johnson’s government looks set to impose a tax hike through an increase in National Insurance (NI) contributions.

The UK Government hopes to increase NI payments by more than 10%, from 12% to 13.25%.

If Ross were to “fall in line behind Boris Johnson to do his bidding” and vote for the NI increase, it would not be the first manifesto pledge which Johnson has broken with the support of the Scottish Tory leader.

READ MORE: Douglas Ross 'deliberately making 400,000 Scots families poorer'

When the UK Government cut foreign aid by almost 30%, from 0.7% of GNI to just 0.5%, Ruth Davidson hit out at her Tory colleagues “who stood on manifesto after manifesto committed to this”, calling them a “bloody disgrace”.

Then, all six of the Scottish Tory MPs voted to break their manifesto commitment. With a vote on a rise to NI to pay for English social care on the horizon, the six seem likely to do so again.

The SNP’s shadow chancellor, Alison Thewliss MP, called on the Scottish Tories not to once again “rubber-stamp Boris Johnson's harmful policies”.

She said: "The Westminster Tory government's tax hike – breaking yet another manifesto commitment – is regressive and will unfairly punish millions of Scottish families, young people, and the low paid.

“The New Economics Foundation has calculated that 2.5 million working households will be affected by both the £20 a week cut to Universal Credit and the increase in National Insurance. On average, they will lose out by £1290 in the next financial year.

READ MORE: Interactive map shows how Universal Credit cuts will hit families across Scotland

"Time and time again, Douglas Ross and his Scottish Tory colleagues have ignored the warnings and shamefully fallen in line behind Boris Johnson to do his bidding – they must at long last find a backbone and vote against these tax plans.

"Refusing to do so will once again see Douglas Ross rubber-stamping Boris Johnson's harmful policies, and imposing them upon the people of Scotland."

Thewliss further warned that Scotland the “toxic tax rise … risks Scotland being sold short and receiving less in return than the money taken from Scottish-based National Insurance payers”.

The Prime Minister claimed that Barnett consequentials will see Scots handed “about 15% more than they would contribute through the levy”, which he called a Union dividend.

The Scottish Tories have been approached for comment.