It’s hard to imagine what Friedrich Engels would make of John McDonnell’s frugal dining habits. Engels, co-founder of Marxism, spent his 70th birthday sharing 16 bottles of champagne and “twelve dozen oysters” — and boasted of his “acknowledged gift for mixing a lobster salad”.

By contrast, McDonnell — perhaps the most famous living Marxist in Britain — is strikingly abstemious. When I ask where he normally eats in Westminster, the shadow chancellor replies: “I don’t really. Not usually.” For lunch today he ate some Rich Tea biscuits.

It is 4pm and we are meeting for a ludicrously early dinner at a café in his constituency of Hayes and Harlington, a gritty multicultural suburb of west London. The veteran socialist usually eschews all corporate hospitality; he has made an exception for Lunch with the FT, but it’s not going to be haute cuisine.