Brexit supporters are right that there is a "democratic vacuum" within the EU, but Britain should remain a part of it in order to overhaul it, Greek economist Yanis Varoufakis has said.
Speaking to ITV News, Greece's former finance minister said while there was plenty to criticise about the EU, leaving it would be of little benefit to the British people.
"The 'Brexiters', people like Boris Johnson, are quite right [that] there is a democratic vacuum in Europe," he said.
"That has to change, and no one in Britain should settle for this democratic deficit, but the only way of getting back your democracy is by staying in and fighting to democratise the European Union."
Mr Varoufakis said he would not "stick up for the awfulness of the European Union that we faced," referring to the prolonged negotiations on the EU bailout for Greece and the austerity measures imposed as part of the rescue package.
But he added: "As rational people we should look to the future with a very simple question - what is going to be better for a majority, a plurality of people in Britain?"
Mr Varoufakis was attending an event called 'Vote In - Another Europe Is Possible' at the Institute of Education in London, where he was speaking alongside Caroline Lucas of the Green Party, Labour MP Clive Lewis and journalist Owen Jones.
All were pushing for Britain to remain in the EU, but making the case for overhauling it.
Ms Lucas, MP for Brighton Pavilion, echoed Mr Varoufakis' comments, telling the crowd:"Europe needs to be more democratic, accountable and transparent - but so does Westminster."
"We need to be in it to change it," she said.
Also at the rally, Mr Varoufakis addressed the issue of immigration, saying he agreed public services in certain parts of the UK were "strained" and people had been left feeling "marginalised in their own country".
But he said that was "not caused by migration, it is merely correlated with it".
"The reason public services are failing is the running austerity feed that promotes a vicious class war against Britain's poor," he said.
Labour's shadow chancellor John McDonnell also spoke at the event, using the opportunity to attack the Tories for dragging the referendum debate "into the gutter".
"We have the opportunity to regroup the referendum debate away from Tory Brexit and into a debate on a democratic Europe," he said.
"A Europe that is not just possible but is urgently and vitally needed - where we can say yes, we are proud of being British, but we are also proud of the European future we have created."