THERESA May has warned Conservative rebels that any attempt to block Brexit will not be tolerated.

The Prime Minister said the date of Britain’s EU exit will be written into law as 11pm – midnight in Brussels – on March 29, 2019.

It comes as Nicola Sturgeon accused the UK Government of leaving Holyrood and the other devolved administrations "substantially in the dark" on key Brexit talks.

The First Minister called on Westminster to make good on its promise to give the devolved administrations a "genuine role" in discussions about exiting the EU, claiming they had instead been "cut out" of the talks.

She said: "In less than 18 months' time, the UK will be leaving the EU, but despite reassurances that all devolved administrations will be consulted on the withdrawal negotiations, we remain substantially in the dark.

"The UK Government assured us that the Joint Ministerial Committee (JMC) would seek to agree UK positions and discuss issues stemming from the negotiations, respecting the devolved competencies, but the UK Government then allowed that process to fall short of what is required."

She added: "This is not an abstract debate about process. Leaving the EU will have an enormous impact on Scottish jobs, our economy and our relationship with the world. Indeed, Brexit's effects are already being felt.

"We know from businesses in Scotland that a hard Brexit will cause serious and long-term economic damage and it is crucial we stay in the single market and customs union.

"As has previously been said, the clock is ticking on Brexit and it is essential that the UK Government live up to its promises to give devolved administrations a genuine role on what is by far the most important issue facing every corner of these islands."

Mrs May is vulnerable to any Tory rebellion, with her slim Commons majority relying on votes from Northern Ireland’s Democratic Unionist Party.

But writing in the Daily Telegraph, she said: "We will not tolerate attempts from any quarter to use the process of amendments to this Bill as a mechanism to try to block the democratic wishes of the British people by attempting to slow down or stop our departure from the European Union."

The EU's chief negotiator Michel Barnier said the latest Brexit talks had made some progress, but more work was needed before the second phase of the negotiations could be green-lit.

Mr Barnier previously said the moment was approaching for a "real clarification" of Britain's position on issues like citizens' rights, the Irish border and the UK's financial settlement.

If the 27 remaining EU members agree next month that sufficient progress has been made on these issues, negotiations will move on to questions of trade and transition to a new post-Brexit negotiation.

The Prime Minister will attempt to win support from European businesses for her goal of moving the negotiations on to trade talks.

She will meet leading business organisations on Monday to set out her vision of a "bold and deep economic partnership" between the UK and EU after Brexit.

Ministers hope that business groups can lobby their national governments to support a trade deal which will be in the interests of both sides in the negotiations.

But in a sign of business unease about the impact of Brexit, motor manufacturers Honda, Ford and Vauxhall set out their concerns in evidence to a Commons select committee.

In a written submission to the Business, Energy and the Industrial Strategy committee, Honda, which employs 4,000 people at its Swindon plant, said it had concerns about disruption to supply chains, regulatory divergence, restrictions on free movement of labour and the impact of tariffs.

Meanwhile, David Davis insisted he will not accept any solution to the issue of the Ireland-Northern Ireland border that damages the "constitutional and economic integrity of the UK".

It comes as Irish Taoiseach Leo Varadkar suggested the only way to avoid a hard border in Ireland after Brexit would be for Northern Ireland to continue to apply the rules of the EU single market and customs union.

But the Irish premier said this did not necessarily mean the UK or Northern Ireland remaining members of either area, suggesting that a "bespoke" arrangement may be reached as part of the Brexit negotiations.