Patrick Heneghan, acting chief executive of Open Britain, has been accused of acting inappropriately towards three female staff members.
Hundreds of thousands have descended on the capital, heading through central London to Parliament Square.
Labour MPs joined protesters as they marched through Brighton demanding another vote on the UK's membership of the EU.
The People’s Vote group says a no-deal Brexit could force half of UK farms out of business.
The Tory grandee said they are fighting for ‘Britain’s national self-interest’.
The People’s Vote campaign wants a referendum on the outcome of Brexit talks.