Boris Johnson has been urged to disclose whether his government has sanctioned any surveillance or intelligence gathering on MPs involved in derailing his Brexit plans.

The extraordinary demand from the Liberal Democrats follows claims published in newspapers that the government had carried out investigations into senior MPs and alleged dealings with foreign governments.

Earlier this month, the prime minister made the claim that MPs behind legislation to avoid a no-deal Brexit on 31 October may have received "legal advice" from other governments - triggering a furious response.

In his regular column for The Independent, Chuka Umunna, the Liberal Democrats' foreign affairs spokesman, said he had written to Mr Johnson demanding clarity over whether any investigation exits or "whether this is an over-briefing from Dominic Cummings and friends."

"This has a strong whiff of the 1930s about it – it is a brazen attempt to suppress dissent and persecute political opponents in parliament by this right wing, nationalist government," Mr Umunna said.

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He added in his letter to Mr Johnson: “In order to ensure parliament can scrutinise HM government’s foreign policy and hold ministers to account for their actions, it is vital for MPs from opposition parties to have dialogue with other governments. It informs our work for the British public, free from interference by HM government."

A briefing to The Mail on Sunday suggested that Downing Street had launched an investigation into alleged links between foreign governments and the MPs behind the Benn Act.

"Sources said No 10 took the unprecedented action after officials received intelligence that the MPs, including former cabinet minister Oliver Letwin, had received help drafting the bill from members of the French government and the EU," the newspaper claimed.

The prime minister was forced to honour the legislation, requesting an extension to the Brexit negotiating period from the EU, as MPs held back from ratifying Mr Johnson's deal during an extraordinary sitting of the House of Commons on Saturday.

In his letter, Mr Umunna also demands the prime minister rules out supporting a bid by backbench Tory MPs to introduce a new law aimed at punishing those who undermine government negotiations abroad.

He said: "I have also demanded he rule out introducing any law seeking to prevent parliamentarians from speaking to other governments – we cannot properly scrutinise government foreign policy if we are prevented from doing do so.

"If he fails to give these assurances, we can take it as a given that another term of a Tory government will be altogether more authoritarian than any government we have seen in a generation."