Theresa May has told MPs there might not be a third vote on her Brexit deal next week if there is insufficient support for it to pass.
If it does not pass, the EU has set a deadline of 12 April for the UK to propose a new plan
Supporters of another EU referendum are due to march through central London later.
Labour’s Tom Watson will speak at the event, pledging to back May’s deal if she agrees to hold a referendum on it.