The leader of Ukip has written to the Queen asking her to suspend parliament until after 29 March to ensure MPs cannot thwart Brexit.

Gerard Batten’s letter also informs the monarch that she should never have approved the 1992 Maastricht treaty as it made her, and everyone else in the UK, citizens of the EU, and was thus unlawful and treasonous.

“Your Majesty’s ministers were gravely in error and wrongly advised you,” states the letter, released publicly by Ukip.

Batten begins by saying he is formally petitioning the Queen under the 1689 Bill of Rights, which established the notion of parliamentary supremacy. He argues the current crop of MPs were elected to uphold the result of the 2016 referendum and thus take the UK out of the EU.

“It is evident that these same members of parliament are attempting by all and any means to thwart this result,” he writes. “They are accordingly in breach of their pledges to you and us, your citizens, and of a longstanding constitutional convention whereby parliament must implement the will of the people expressed in a popular vote, and are bound by electoral manifestos which have received popular assent at general elections.

“Therefore, I ask Your Majesty to thwart their efforts and to prorogue parliament from now until after 29 March 2019, which is the agreed date set aside in the Withdrawal Act of Parliament of 2018 when the United Kingdom will leave the European Union.”

Batten is not the first politician to raise the idea but is the only one to have done so seriously. During a Brexit debate last week a Conservative backbencher, Desmond Swayne, proposed it to Theresa May, but apparently as a joke.

In his letter, Batten also warns the Queen about the Maastricht treaty, which brought closer integration with the EU and which passed into UK statute in 1992.

“This treaty and statute purport to make Your Majesty a citizen of the European Union,” he writes. “The treaty states that Your Majesty as a citizen of the union will ‘enjoy the rights conferred by this treaty and shall be subject to the duties imposed thereby’.

“To presume to convey rights on or to impose duties on Your Majesty was, and remains, unlawful and treasonous under the Bill of Rights and the coronation oath. Your Majesty’s ministers were gravely in error and wrongly advised you.”

Batten, who took over as Ukip leader after the brief and disastrous tenure of Henry Bolton, has steadied the party financially but has also seen a series of leading members – among them Nigel Farage – quit due to his increasingly hard-right stance.

Batten has repeatedly focused on Islam, which he refers to as a “death cult”, and has proposed policies including special checks on immigrants from Islamic countries and the possibility of Muslim-only prisons. He appointed Tommy Robinson, founder of the far-right English Defence League, as an adviser.