If I thought I had the ear of Mrs May this is what I would have written to her this day as she takes the country down the most dangerous of paths:
Dear Prime Minister,
This weekend I had the pleasure of joining the tens of thousands of people marching in London against your vision of a Britain after Brexit.
A sun-soaked Parliament Square provided a brilliant back drop to what was also a celebration. As you know, this weekend marked the anniversary of the Treaty of Rome, and while we marched in London your European contemporaries met in Rome to mark 60 years of peace in the EU.
Our celebrations in London were of course tinged with sadness and fear as we prepared ourselves for you to hit the self-destruct button by triggering Article 50 to formally begin the Brexit process.
Your version of Brexit - a so called 'Hard Brexit' - does nothing to unify the 48% with the 52% and shows you are willing to take our country into an unknown land without even considering meaningful negotiations with the EU.
As the clock is ticking towards a hard Brexit, the swell of support on Saturday shows we're not prepared to roll over and accept this situation. We're fighting for membership of the Single Market, and we're also underlining the point that democracy didn't end on 23 June - a Hard Brexit wasn't on the ballot paper and the people deserve to be consulted again with a vote on the terms of the deal.
Mrs May, the thousands there on Saturday have made a commitment to be with you every step of the way, holding you to account on your decisions and pushing for a vote on the terms of the deal.
This is why I am so concerned you cannot answer some of the most pressing questions about the Brexit negotiations.
When you made your opening gambit back in January with your speech to a Diplomat-stuffed room, what struck me was the lack of certainty to your plan and that's why I wrote to you then with five of my main concerns, which I shall list once more below:
I raised my concerns about the hundreds of vital environmental protection regulations that should not be eroded and that we needed to know the cost of these.
I asked whether you aimed to maintain programmes such as Erasmus to help students live, work and study across Europe.
I asked how you were aiming to protect Britain's position as one of the best places in the world for science and innovation - what would your government do to fill the gap left from EU funding being withdrawn and how do you aim to ensure full access to EU science collaboration?
I asked how you would deal with cross border trade outside the EU; as we will no longer have access to these agreements under your hard Brexit plan, how does this Government plan to quickly replace these lost agreements?
And finally, I asked what action do you plan to take to ensure criminals can be brought back to Britain and others deported speedily to face justice.
Prime Minister, please reconsider your hard line - you have failed to answer some of the most pertinent of questions about this process and that fills so many of us with dread.
As one of the UK's directly elected members of the European Parliament I can tell you that your approach has been met with incredulity by our partners across the Union. My friends and colleagues cannot understand the stance you have taken and your hard-nosed approach before the negotiations have even begun.
They are not only saddened at losing a friend but they are worried about Brexit hitting them and their countries in their pockets, and concerned about nationalist elements in their own countries.
But their main priority is keeping the EU together, stopping the tide of nationalism and preventing Brexit from stealing the next two years on the EU's agenda.
This means you are entering very turbulent territory indeed - playing hard ball will only serve to weaken your position, not strengthen it.
This climate makes securing a deal within the two-year window which your Brexit ministers have argued a pipedream.
What does your line mean for British business, British science or for British people? Extra cost, uncertainty, more time when hatred and vitriol rises in the growing chasm between the two sides. A country unable to move on from the debate.
If I may, Prime Minister, I would like to give you one tip: European politics is a different ball game to British politics. Europeans form coalitions, work with people and that's how the EU has effectively built free trade agreements with 53 markets across the world.
In order to get any sort of good deal for Britain we need friends, not enemies; you should be reaching out, not turning your back or stamping your well shod feet. British expectations should be realistic from the outset.
The most worrying part of your speech back in January was your assertion that no deal was better than a bad deal - but as all businesses, banks, governments and the WTO have said - this would be a disaster for Britain and our economy.
Please Mrs May, consider the perils of a no deal and take the advice from a fellow British politician experienced in European politics. Instead of threatening, work constructively and cooperatively and you will be met with a readiness to negotiate a deal that works for both sides.
Catherine Bearder is the Liberal Democrat MEP for South East EnglandSuggest a correction