Britain may not be in a position to trigger article 50 to begin leaving the European Union by the government’s deadline at the end of March, the prime minister of Malta has said.

Joseph Muscat, whose country takes over the EU’s rotating presidency in January, also warned that EU leaders were “not bluffing” when they insisted Britain would not have the single market access it now has if it also wanted to curb immigration, adding that the European parliament could veto any deal.

The supreme court will hear in early December a government appeal against a high court ruling that parliament must be consulted before article 50 can be invoked, which Theresa May has promised will happen before April.

Muscat told the BBC he would “not be surprised” if the legal proceedings resulted in the divorce process being delayed, particularly since the supreme court could in theory decide to refer a final decision to the European court of justice.

He said article 50 negotiations would necessarily be complicated, with agreement needing to be reached on a range of issues including the size of the UK’s leaving bill, the question of the border between the UK and the Republic of Ireland, and interim security arrangements.

Only then could talks start on the nature of the new relationship between the EU and the UK, Muscat said, warning that Britain should not take lightly EU leaders’ warnings that Britain could not expect to limit freedom of movement and retain some form of single market membership.

“In giving a good deal to Britain, the EU will not want to jeopardise its own single market,” he told Radio 4’s Today programme. “We are all going to lose something but there will not be a situation where the UK has a better deal than it has now. It’s simply not going to happen.”

Muscat was openly dismissive of repeated suggestions by the UK foreign secretary, Boris Johnson, that Britain would be able to control free movement and enjoy privileged single market access.

“And I could win the Olympic 100 metres,” he said. “All of us have been pretty clear in our approach that we want a fair deal for the UK, but that kind of fair deal can’t translate itself into a superior deal.”

He added: “There is absolutely no bluffing from the EU side, at least in the council meetings I have attended, saying ‘we will start in this position and then we will soften up’. No, this is really and truly our position and it will not change.”

Muscat warned that talks could get “messy”, saying that since it was considered fair game in the UK to bash Brussels, Britain should “not be surprised when in Brussels they bash you back”.

He also said that as someone who knew Britain well and had studied there, he found it “hard to believe that the British civil service doesn’t have this all sorted out”.

Muscat said that even once a final deal or interim agreement was reached at the end of the two-year negotiating period between the 27 countries of the EU and the UK, the European parliament could decide to veto it.

“The real threat for me is the parliamentary elections in 2019,” Muscat said. “I think there is a clear and present danger of anything that we would have done being scuttled at the end of the process – for the parliament to veto it. It will get complicated. Divorces are never easy, I think.”

May’s spokesman told reporters that the prime minister remained confident of being able to trigger article 50 as planned.

Asked about Muscat’s comments on single market access, he said: “We have been very clear on this to date – this is a negotiation that will take place next year, and the government will set out its negotiating strategy in the fullness of time.

“The aim of that negotiation is to get the best possible deal for Britain’s companies to access and work with and within the single market, and for European businesses to have the same access here.”