Theresa May will finally lift the lid on her Brexit strategy next week – possibly just days before a crucial Supreme Court ruling on whether Parliament must give its consent to leaving the EU.

A long-awaited speech – which, the Prime Minister promised, would reveal “more details” of her plans – will be made next Tuesday, it was announced.

Downing Street has decided to get ahead of a likely defeat in the Supreme Court, which is expected to confirm that MPs and peers must approve the triggering of the Article 50 exit clause.

The Government is believed to have already drawn up at least two versions of a Bill that could be tabled to comply with the ruling – which could come later in the week.

In the speech, the Prime Minister will be under pressure to finally state clearly whether she wants Britain to remain in the EU’s single market or customs union after Brexit.

Angela Merkel, Germany’s chancellor, has led EU leaders who insist Britain cannot enjoy favourable access to the single market if it ends free movement of people.

Last weekend, Ms May gave her clearest signal yet that single market exit is therefore inevitable – in order to achieve border controls – but stopped short of saying so.

Even her hints were enough to send the pound to its lowest level since October, as the markets interpreted her remarks as evidence of a looming “hard Brexit”.

She said: “Often people talk in terms as if somehow we are leaving the EU but we still want to kind of keep bits of membership of the EU.

“We are leaving. We are coming out. We are not going to be a member of the EU any longer. So the question is what is the right relationship for the UK to have with the European Union when we are outside?”

Fresh in the memory is the fierce criticism of Sir Ivan Rogers, the UK’s ambassador to the EU, who condemned “muddled thinking” in his explosive resignation letter.

The Prime Minister will also be under pressure to say whether she will seek a transition deal, to avoid the economic damage from crashing out of the EU without a fresh trade agreement.

Cross-channel security and the future status of three million EU citizens in the UK are other key issues that she has been urged to address.

Today, her official spokeswoman said: “She will be making a speech on Tuesday, setting out more on our approach to Brexit, as part of preparing for the negotiations and in line with our approach for global Britain and continuing to be an outward-looking nation.”

However, ministers have said the Brexit plan – demanded by the Commons in a vote last month – will not be published until February, at the earliest.

It has been suggested that the Government expects to lose by seven votes to four, when the 11 Supreme Court judges rule on Article 50.