The prime minister will issue a call for unity as she starts the countdown to Britain's exit from the European Union today.

Theresa May will tell MPs that Britain's shared values, interests and ambitions can bring it together as it faces a 'momentous journey'.

She will address the House of Commons after Sir Tim Barrow, the UK's permanent representative to Brussels, has personally handed over a letter to European Council president Donald Tusk starting the clock ticking on two years of Brexit negotiations.

'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,' she will tell MPs.

'It is my fierce determination to get the right deal for every single person in this country,' she will add.

Senior Conservative Euro MP Vicky Ford warned there was a 'huge amount of work to be done in the months ahead if we are to achieve an amicable separation from the EU'.

The Eastern region MEP, who has recently met Brexit secretary David Davis, European Commission chief negotiator Michel Barnier and Guy Verhofstadt MEP, who is coordinating the European Parliament's resolution, said she had been impressed by the goodwill demonstrated by colleagues from across Europe.

But warned some would seek to cause disruptions for their own political gains.

But Labour MEP Alex Mayer said today would be a 'sad day when Britain finds itself on the wrong side of history'.

'This is a backwards step which ultimately will make our country weaker, poorer and more isolated. I certainly didn't come into politics to make people's lives worse so when I see our country hurtling headlong down the wrong track I call it out.'

Conservative MEP and leading Brexit campaigner David Campbell-Bannerman he had a feeling of 'relief and gratitude' to the British people for having the sense to vote Brexit, as Article 50 is triggered. He said Brussels had initially been stunned, but there was now a sense of realism in the European Parliament.