Analysis of a tweet sent by the Prime Minister shows ­­that an earlier version had a reference to the current US President.

The words ‘Trump on his’ can be seen in the image when the brightness and contrast are adjusted, with other eagle-eyed Twitter users said they spotted ‘second term’ and ‘the future’ in a smaller font size.

Johnson sent his congratulations to the President Elect and Vice President Elect Kamala Harris on November 7, an hour after victory was taken by Biden.

He tweeted: ‘Congratulations to Joe Biden on his election as President of the United States and to Kamala Harris on her historic achievement.

‘The US is our most important ally and I look forward to working closely together on our shared priorities, from climate change to trade and security.’

The hidden message was brought to prominence by the Guido Fawkes blog.

Among those reacting to the gaffe was Labour MP Angela Rayner, who tweeted: ‘Looks like No 10 could do with a few more staff who have trained in “cyber” (they just didn’t know it yet).’

Downing Street told the Mirror that a ‘technical error’ meant that parts of an alternative message were embedded in the graphic. However, the spokesman did not explain what the technical error was.

A spokeman said: ‘As you’d expect, two statements were prepared in advance for the outcome of this closely contested election. A technical error meant that parts of the alternative message were embedded in the background of the graphic.’