The Communist Party of Britain (CPB) will not be standing candidates in the general election for the first time since the 1920s, it emerged on Monday 24 April.
The roughly 700-strong party is instead urging its supporters to back Labour and Jeremy Corbyn at the ballot box on 8 June.
"Labour's policies in this election include more progressive taxation, state bank investment in public services, support for industry, an end to NHS privatisation, public ownership of the railways, community ownership of energy, an end to zero-hours contracts, the restoration of employment and trade union rights and building half a million new council houses," said Robert Griffiths, general secretary of the CPB.
"The Communist Party is in no doubt that this second option is the only one that serves the interests of workers and their families. Therefore our members will be campaigning for a Labour victory as the essential first step towards the formation of a left-led government at Westminster."
Despite the endorsement, Corbyn is not expected to become prime minister after the general election. The latest opinion poll from YouGov, of more than 1,500 people between 20 and 21 April, put Labour 23 points behind the Conservatives (48% versus 25%).
Liberal Democrat MP Alistair Carmichael said: "From 1920 to 2017 the Communist Party of Great Britain elected five MPs. They have obviously concluded they can continue in that tradition by backing Jeremy Corbyn's Labour Party. I think that they are probably right about that."
The Communist Party of Britain split from the now defunct Communist Party of Great Britain in 1988. A Labour Party spokesperson told IBTimes UK: "Even a stopped clock tells the right time twice a day."