Appearing on The Andrew Marr Show before her speech on Brexit at the Conservative Party conference in Birmingham at the weekend, May said, "As you know, I have been saying that we wouldn't trigger it before the end of this year so that we get some preparation in place.
"But yes, I will be saying in my speech today that we will trigger before the end of March next year."
"This is about delivering for the British people. It is not just about leaving the EU, it's about people's trust in politicians. The people have spoken, we must deliver.”
Michael Izza, ICAEW chief executive
There is an acceptance that these negotiations will take time but the i’s must be dotted and t’s must be crossed to ensure the UK gets the best deal possible
The minimum period for leaving the European Union after Article 50 has been triggered is two years so it is possible that the UK will leave the European Union in Spring 2019.
Once Article 50 is triggered, negotiations over the UK’s future relationship with the EU will begin.
May said she wants to get “the right deal” from its negotiations with the EU.
“We want to negotiate with them what the relationship will be. Life is going to be different in the future. Crucially we want to still have a good relation with the European Union,” she said.
“The process of leaving the European Union is quite complex. There is complexity in our relationship. I think we owe to people here in the UK in terms of their jobs and for businesses who want to invest in our future, to ensure we get the right deal."
"The remaining members of the EU have to decide what the process of negotiation is," May added.
"I hope, and I will be saying to them, now that they know what our timing is going to be - it's not an exact date but they know it will be in the first quarter of next year - that we'll be able to have some preparatory work so that once the trigger comes we have a smoother process of negotiation.”
Donald Tusk, president of the European Council tweeted, “PM May’s declaration brings welcome clarity on start of Brexit talks. Once Article 50’s triggered, E127 will engage to safeguard its interests.”
Businesses have urged the government to take its time on getting the right EU deal.
A survey by ICAEW has found 80% of companies want May to bide her time before starting Brexit negotiations in order to ensure Britain secures the best possible exit terms, rather than striking a deal as soon as possible.
Those surveyed said the free movement of goods, services and capital between the UK and the EU is very important when it comes to their own business for 37%, followed by the free movement of people between the UK and the EU (23%) and the freedom for the UK to negotiate trade deals and set tariff levels with non EU countries (23%).
Ending of compliance with EU laws and regulation was the least important for respondents.
Around a third of businesses said they think the EU referendum result and on-going discussions will have a fairly negative impact on their business (36%), customers (34%) and suppliers (35%) in the year ahead.
However, nearly half (48%) of those surveyed are fairly confident the government will be able to strike a deal with the EU that is good for their business, while 30% are not very confident.
Michael Izza, ICAEW chief executive, said, “The UK government should be under no illusion of the uncertainty that Brexit has caused and is causing for businesses.
"However, companies are not prepared to exchange that uncertainty for a deal with the EU that is rushed and could have unintended long term consequences.
"There is an acceptance that these negotiations will take time but the i’s must be dotted and t’s must be crossed to ensure the UK gets the best deal possible.”
“Government should not take its eye off the economic ball while the negotiations with the EU are ongoing, as post-Brexit Britain will require strong policies aimed at driving economic growth.
"Just like a business, government needs to focus equally on growing its revenues while also keeping costs under control. The Autumn Statement will be the perfect opportunity for Philip Hammond to start to rebuild business confidence.”