Mr Johnson’s allies claimed Mr Stewart’s targeting of their man bore all the hallmarks of the fierce competitiveness instilled in pupils at the elite school.
Mr Stewart, who at 46 is eight years younger than his rival, also followed him to the same Oxford University college – Balliol.
Rory Stewart’s attacks on his Tory leadership rival Boris Johnson have been blamed on ‘classic Old Etonian rivalry’
The two men both went on to serve at the Foreign Office, although Mr Stewart was a junior diplomat compared to Mr Johnson’s stint as Foreign Secretary.
The International Development Secretary has criticised Mr Johnson, insisting he could never serve under him and branding him an untrustworthy ‘Pinocchio’
In the past week, the International Development Secretary has criticised Mr Johnson, insisting he could never serve under him and branding him an untrustworthy ‘Pinocchio’.
Last night, one Minister backing Mr Johnson said: ‘This level of rivalry has a classic ring to it.
‘It’s just an Eton thing and, to be honest, a Balliol thing as well.
‘You only truly despise someone who is very similar to you but always destined to go one better.’
Friends of Mr Stewart dismissed the rivalry claim as ‘absurd’.
Tory insiders say some of the party’s MPs are impressed by Mr Stewart’s ‘competence’, contrasting it with ‘gaffe-prone’ Mr Johnson.
But Mr Johnson’s backers point out that Mr Stewart is also accident-prone, recalling that as a newly elected MP in 2010, he had to apologise after branding some areas of his Cumbrian constituency ‘pretty primitive’, with ‘people holding up their trousers with bits of twine’.