Britain is set to trigger the Brexit process before March of next year, Theresa May has announced.

The UK looks set to leave the European Union by summer 2019 after triggering the formal process to pull out in the coming months.

The Prime Minister said Article 50 of the Lisbon Treaty will be triggered in the first three months of 2017, marking the start of the two-year process to enact Brexit.

The process can be extended beyond two years if Britain and all other EU countries unanimously agree, but that prospect is seen as unlikely.

She made the announcement after revealing plans for a "Great Repeal Bill" to transpose all EU law applying to the UK into domestic law, ready for the day the country leaves the union.

Ahead of her speech on Brexit at the Conservative Party conference in Birmingham, Ms May told BBC One's Andrew Marr Show: "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 (Article 50) before the end of March next year."

Ms May added: "The remaining members of the EU have to decide what the process of negotiation is.

"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.

"It's not just important for the UK but important for Europe as a whole that we're able to do this in the best possible way so we have the least disruption for businesses, and when we leave the EU we have a smooth transition from the EU."

Ms May said Parliament will be kept informed, adding: "This is not about keeping silent for two years, but it's about making sure that we are able to negotiate, that we don't set out all the cards in our negotiation because, as anybody will know who's been involved in these things, if you do that up front, or if you give a running commentary, you don't get the right deal."

The Prime Minister was challenged on how she will seek to control immigration after Brexit. She was asked if a work permit system would be adopted for skilled workers.

Ms May said: "We will look at the various ways in which we can bring in the controls that the British people want, and ensuring, as we have been in our immigration policy generally, that the brightest and best can come to the UK."

She will later tell the Tory party conference that her "Great Repeal Bill" will scrap the 1972 European Communities Act, which gives direct effect to all EU law, and at the same time convert Brussels regulations into domestic law.

This will give Parliament the power to unpick the laws it wants to keep, remove or amend at a later date.

Brexit Secretary David Davis will also tell the conference: "To those who are trying to frighten British workers, saying 'when we leave, employment rights will be eroded', I say firmly and unequivocally, 'no they won't'."

A spokesperson for Michael Russell, the Scottish Government's minister for UK negotiations on Scotland's place in Europe, said: "Despite the hype Theresa May's announcement tells us nothing new about the process and does nothing to remove the suspicion that the PM is being pushed into a hard Brexit against the economic interests of the country.

"One hundred days on from the referendum and with up to six months until the triggering of Article 50 it is time the government got serious and put our economic interests and membership of the single market at the front of their negotiating plans.

"With a clear majority in the Scottish Parliament for retaining membership of the single market - expressed as recently as last week - it is difficult to‎ envisage the circumstances in which the Scottish Parliament would give consent to any legislation that did not guarantee this."