It comes after Rishi Sunak attacked Sir Keir for taking £1.5 million in donations from Mr Vince, who has also pledged tens of thousands to Just Stop Oil.
Conservative MPs have capitalised on the unpopularity of the the environmental group and its stunts to attack Sir Keir for accepting money from him.
‘I can’t not speak out’
Mr Vince said: “I’m here to support the incredibly brave people of Just Stop Oil. They put themselves and their liberty on the line.
“I support them in other ways, in the media and with donations, but I thought I would do more.
“I can’t imagine it will make much difference to Keir Starmer, he’s his own man and so am I. I hope it doesn’t harm [Labour] but I can’t not speak out.”
He posted a photograph of himself outside Parliament with a message to the Prime Minister, writing: “I’m in London, where are you?”
Starmer attacked by Tory MP
Mr Sunak is in Washington DC meeting US President Joe Biden.
Greg Smith, the Tory MP for Buckingham and a member of the transport committee, attacked Sir Keir over his links to Just Stop Oil.
“We know where we stand with Labour – the party of shutting down London and shutting down work.
“This is going to cost people significant money, significant time both commercially, work wise and those that will have spent a lot of money to come into London to see some of our attractions, or maybe go to the theatre, and end up being frustrated and potentially miss what they’re coming down for.”
