He said he found it "surreal" that he had youthful acquaintances with the leaders of both major parties, having been at school in Surrey with Starmer and at Oxford University with Boris Johnson, but said the Labour leader had “obviously matured” since his youth while the prime minister “seems incapable of that”.
Describing himself as “an uptight young Thatcherite” in his youth, Sullivan recalled furious arguments with the left-leaning Starmer.
But he said the pair also bonded over their shared love of manic comedy team Monty Python, and were still in touch years after leaving school.
Describing the 1980s Johnson as “a charming bullsh***er”, the journalist said: “I liked him because he made me laugh, didn’t take himself too seriously, and wouldn’t compensate or apologise for his ridiculous toffishness, which was a nice change from all the other Etonians.”
But he added: “I was closer to Keir. Every morning, we both took the 428 and 410 buses, if I recall, from our respective homes, East Grinstead and Oxted, to Reigate Grammar.
“I was a diminutive, bespectacled, very uptight young Thatcherite, and Keir was a near-Bolshevik bruiser, with a Bay City Rollers haircut, a fat tie, an unbuttoned collar and an air of real roughness.
“The arguments began on the bus, and got more intense in 1975, when Thatcher became Tory leader, escalating through to 1979, when Keir and I were all but screaming at each other on a daily basis.
“It wasn’t all politics, of course. The morning after the previous night’s Monty Python, we’d be trying to remember the best lines, shouting over each other, to the general consternation of the good local folk of Godstone and Redhill.”
Looking back on the years since his 1970s schooldays, Sullivan added: “I guess we both mellowed. But Keir also transformed himself into someone far more polished and professional than I remember.
“The difference between him and Boris is that Keir has obviously matured, and Boris seems incapable of that. Keir, for his part, still loves hanging out with his old mates, has made time to stay in touch, and we’ve had some lovely reunions.”