However, he said that the party has “reverted to type” since it won control of the Welsh parliament, known as the Senedd, from Labour in May after 27 years in power. Labour has controlled the Welsh government since the introduction of devolution in the late 1990s.

Kinnock said he believes Plaid Cymru’s “mask has slipped,” after its Leader Rhun ap Iorwerth met Scottish First Minister John Swinney and Sinn Féin Vice President Michelle O’Neill earlier this month to discuss greater cooperation on achieving independence.

Opinion polling since Andy Burnham became prime minister in July suggests currently no one party would win an overall majority after the next election.

However, Kinnock suggested the price Plaid Cymru could demand for support in the House of Commons could make arrangements untenable: “If the condition for that coalition to work is that you would then agree to nationalism and separatism and the breakup of the United Kingdom, the answer is no, because that is fundamentally about our values as a party that believes in our precious union.”