The man who brought Ulez to London cannot fail but to be impressed by a man who has doubled down on net zero and renewables after a major blackout last year.
Spanish electricity prices are lower than in the UK, well under the EU average and less than a third of Italy’s.
Mr Sánchez is not squeaky clean, despite spearheading some of Europe’s most progressive laws.
He is an inveterate political gambler with a keen nose for power and possessing an opportunist streak.
His political opponents call him “dog” – a pun on his first name – because he has proved so hard to remove.
Sir Keir could still be brought down by the Mandelson scandal. Mr Sánchez is embroiled in corruption allegations aimed at his closest allies – his brother and his wife, who both deny accusations against them – but is still going strong.
The gloves have long since come off in the polarised world of Spanish politics, where the centre is increasingly a no-man’s-land.
A conviction politician
Sir Sadiq may be itching to pick a similar fight with the Tories and Reform, who he accuses of dancing to the tune of the far-Right.
Mr Sánchez lost the popular vote at the last election but still stayed in office.
He is skilled at using Spain’s culture war between Left and Right to glue together his broad coalition of Leftists, separatists and former terrorists in a united front.
The Prime Minister, Sir Sadiq might reflect, struggles to deal with the far less formidable prospects of Wes Streeting and Andy Burnham.
In Madrid, Sir Sadiq came face to face with a conviction politician who has a very good chance of winning another term as prime minister.
The contrast with his party leader, Sir Keir, must have been painfully stark.