Boris Johnson will stamp major schemes in Scotland that are paid for directly by the UK Government with a Union flag from next year, The Telegraph can reveal.
The flag will replace the European Union symbol, which has been used to denote when a bridge or road has been directly funded by Brussels.
The idea has been backed by the new Scottish Conservative leader, Douglas Ross, who said Tories north of the border needed to be "unashamed of our investment in Scotland".
But it was greeted with dismay by senior SNP politicians, with one accusing Mr Johnson's Government of "posturing of the worst order" and "trying to force the union flag down people's throats".
The Union flag will be used to highlight when UK central Government money has been spent in Scotland. It will not apply to Scottish government spending, even though a proportion of that derives from an annual block grant from London.
Mr Ross said he wanted to show the "visual connection" between UK Government money and schemes in Scotland.
In an interview with Friday's edition of Chopper's Politics, which you can listen to on the audio player below, he said: "We should be unashamed of our direct investment in communities across Scotland.
"We will see that, through the shared prosperity fund, that is the money that the EU used to earmark for projects in Scotland and other parts of the UK.
"If they could have an EU flag on it, why not have the United Kingdom flag on it to show that here is an example of our two governments in Scotland, working together, and the UK Government delivering for individual communities and projects the length and breadth of the country?"
Mr Ross said UK support "has seen us through the Covid pandemic by supporting local economies... the VAT reduction to five per cent is as welcome to tourism and hospitality companies in Shetland as in south Cornwall".
On Thursday night, Alister Jack, the Scottish Secretary, said the plan had been signed off by both Mr Johnson and Michael Gove, the Cabinet Office minister, and would start next year after the end of the Brexit transition period.
Mr Jack told The Telegraph: "Where there is direct investment or joint investment between the two governments, you would expect to see the Union Jack sitting alongside the Saltire."
However, he admitted that SNP supporters were likely to be put out by the appearance of union flags on bridges and roads in Scotland. "They never got upset about seeing a European Union flag sitting alongside the Saltire – it is the only the Union Jack that upsets them," he said.
Tommy Sheppard, a senior SNP MP, described the plan as "foolish, and political tokenism and posturing of the worst order".
He said: "It would probably be counterproductive because there is no point trying to force the union flag down people's throats in the hope that they would like it. If the Union is so great, they should not need constantly to use the flag to promote it."
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