Ada Colau, mayoress of Barcelona congratulates Sadiq Khan on taking the reins in London

Ada Colau of the Podemos faction known as Barcelona En Comú – part of the wider Catalunya regional branch of Podemos, En Comú Podem – said it was 'great news' that a 'capital city the size of London' had chosen a Muslim from a working-class background and who is 'dedicated to protecting human rights and equality in Europe'.

In a separate announcement in English, Colau said Barcelona was 'ready to work alongside London' on human rights and social justice in cities.

Sadiq Khan (pictured), 45, is one of eight children born to Pakistani immigrants in the working-class borough of Tooting.

Khan was born within a few months of his parents' arrival in the UK, where his mother was a seamstress and his dad a bus driver.

The new Lord Mayor of London, who replaces the outgoing Boris Johnson, started work at a very young age and continued doing so all the way through university.

His law degree led to a job at Louise Christian Solicitors, which specialised in human rights, and changed its name to Christian Khan Solicitors when Sadiq was made a partner.

Khan's passion for defending the underdog eventually led him to the House of Commons at the age of 33, with the backing of former Labour prime minister Gordon Brown.

The Labour MP suffered an anti-Islam campaign by his Conservative rival Zac Goldsmith, who is said to have implied Khan supported terrorism – but with 57% of the votes and more than any other mayor of London to date, the alleged smear actually worked in his favour.

He was photographed at his swearing-in ceremony along with his wife Saadiya Khan (née Ahmed), where guests of honour included Baroness Doreen Lawrence whose son Stephen was shot by police in London five years ago.

Khan, unlike his predecessor Boris Johnson, is totally against a Brexit and warns it could put well over a million jobs in London at risk, especially those in the City.