The Prime Minister will explicitly pledge to represent EU nationals in the UK in the negotiations ahead after months of criticism at her failure to guarantee their future rights. On the eve of Britain triggering Article 50 of the Lisbon Treaty, Michel Barnier, the EU Commission’s chief Brexit negotiator, underlined the importance of the issue to the remaining member states with a commitment to be “firm” on the rights of EU citizens in the UK. A letter, signed by the Prime Minister, will be hand-delivered to the European Commission on Wednesday setting out Britain’s approach to the talks which are supposed to be completed within two years. In a statement to MPs, Mrs May will repeat her call for the country to unite to make a success of Brexit. She will say: “When I sit around the negotiating table in the months ahead, I will represent every person in the whole United Kingdom – young and old, rich and poor, city, town, country and all the villages and hamlets in between. “And yes, those EU nationals who have made this country their home. “It is my fierce determination to get the right deal for every single person in this country.” Speaking on the day after the Scottish Parliament agreed to demand a fresh independence referendum, a call the Prime Minister has already rejected, Mrs May will described the UK as “one great union of people and nations with a proud history and a bright future” . “We all want to see a Britain that is stronger than it is today. We all want a country that is fairer so that everyone has the chance to succeed. “We all want a nation that is safe and secure for our children and grandchildren,” she will say. While Mrs May’s letter will start the Brexit process, Europe’s formal response will not come until after a special summit next month. But securing the rights of EU nationals and agreeing the sum to be paid by the UK Government to settle its liabilities are known to be among Brussels’ top priorities. Writing on Twitter, Mr Barnier said Brexit “made EU citizens worry about their future” and that the “EU will be firm on their rights”. Article 50 will be triggered amid renewed warnings over the consequences for the UK if the two-year process ends with departure from the European single market and no trade agreement with the EU. Sheffield Hallam MP Nick Clegg, the Lib Dems’ Brexit spokesman, said: “Theresa May is risking taking us out of the world’s largest market without any idea whether new trading relationships will be in place.”