The initiative has been coordinated by "Grassroots for Europe", a network of local activist groups across the UK and beyond, in what is fast becoming the EU's largest pro-European mass movement.
The letter was hand delivered on Sunday, 25 November 2018, to Mr Tusk's office to coincide with the EU Summit, which had been arranged to finalise the Withdrawal Agreement. It calls on him to recognise that the Prime Minister, who was also in Brussels, does not represent the majority view - and that more and more people are turning against Brexit as they've come to understand its implications.
More than 160 grassroots groups campaigning to stop Brexit have sprung up since the 2016 referendum in towns and cities across the UK. Supporters of the campaign took part in an unprecedented mass demonstration in London last month, when 700,000 people marched on Parliament to demand a People's vote on the Government's Brexit deal, with an option to remain. Since then publication of the UK/EU withdrawal agreement has sent shock waves across the political landscape and the possibility that Brexit might not happen at all has begun to be widely accepted. The Prime Minister herself has finally admitted this is a possibility, and last week Donald Tusk commented that a "no Brexit scenario" was still on the cards.
The letter cites recent opinion polls suggesting 54% of British people would now vote remain concluding "As representatives of a substantial - quite possibly majority - view of ordinary British people, from all parts of our kingdom, we now ask you to please hear our voices and realise that the mood in the UK has moved against Brexit.
"In this context, we urge you to keep open the possibility of Article 50 being revoked and the UK remaining in the European Union"
The Withdrawal Agreement is expected to be put before the UK Parliament in mid December. However, it appears to have very little chance of being approved by MP's. If there is then a stalemate in Parliament, campaigners believe that a fresh People's Vote with an option to stay in the European Union will emerge as the only viable solution.
The full text of the letter can be accessed here.