Mayoral candidate Caroline Pidgeon has said it would be "insane" to leave the EU, responding to news that Britain will vote on a referendum on June 23.
The Liberal Democrat candidate said she will make the case for Britain to stay in the EU.
Continued British membership of the European Union is "crucial" to London's future success, according to a new report by a leading business organisation in the capital.
The report for London First warned that the city will suffer if the UK votes to leave in the referendum promised by David Cameron for 2017,
Mayor of London Boris Johnson has said the UK needs to 'think globally' if it is to succeed and says restrictions imposed on Europe by Brussels is preventing growth.
Speaking from the Global Investment Conference in the capital he said that what he and what he thinks the Prime Minister, wants to see is a renegotiation of the rules imposed on Europe by Brussels.
He said the 'micro-climate of gloom' in the eurozone has been caused not just by the Euro but by the rules and regulations created over the past few decades by Brussels which Boris Johnson says is holding back growth.
The Mayor of London said a renegotiation is needed to 'get rid of some of that nonsense'.
"If that fails, then yes obviously we should be ready to walk away, I don't think that is as existential, as dramatic a step as it was perhaps 10 or 20 years ago." - Boris Johnson
The March of the Beekeepers through Parliament Square comes ahead of a major vote in Brussels on Monday. Environment Secretary Owen Paterson is expected to vote against a ban on some neonicotinoid pesticides, which campaigners say are contributing to a decline in bee populations.
Boris Johnson has branded the EU's proposed bonus cap a "deluded" and "self-defeating" policy.
The Mayor claims that limiting bonuses to a maximum of twice a banker's salary will only serve to boost financial centres outside the EU.
He said: "People will wonder why we stay in the EU if it persists in such transparently self-defeating policies. Brussels cannot control the global market for banking talent. Brussels cannot set pay for bankers around the world.
"The most this measure can hope to achieve is a boost for Zurich and Singapore and New York at the expense of a struggling EU. This is possibly the most deluded measure to come from Europe since Diocletian tried to fix the price of groceries across the Roman empire."
Leaving the European Union would not be "the end of the world" for Britain, London mayor Boris Johnson has said.
Mr Johnson - seen as a possible future rival to David Cameron for the Tory leadership - said that the Government could not put off indefinitely a referendum on Britain's future in the EU.
In an interview with BBC1's The Andrew Marr Show, he said that he would like to see the public given the chance to vote on the issue before the next general election in 2015 although he did not expect it to happen.
Boris Johnson has called for a referendum on whether the UK should stay in the European Union, saying he wanted to be friendly with Europe but free to trade with the rest of the world.
In a speech to news agency Reuters, the Mayor called the Euro "a calamitous project" and said he believed the government needed a change of tactics in order to give London and the rest of the UK the best chance to thrive in the global economy.