The prime minister has told BBC Wales he does not know whether he will campaign in Caerphilly ahead of the Senedd by-election next month.

Sir Keir Starmer appeared to give his party’s conference at the weekend as a reason why he may not go to the constituency.

Labour faces a fight to retain Caerphilly, which it has held in the Senedd since 1999, and in Westminster since the early 20th century.

The prime minister said there were “huge benefits” to having Labour in power in both the UK and Welsh governments, and that his party has to work hard to “earn every vote”.

Senior figures in political parties often take part in by-election campaigns to help teams on the ground.

The by-election, triggered by the death of the late Labour Member of the Senedd (MS) Hefin David, takes place on 23 October.

Sir Keir’s comments came as the UK government announced a Great Britain-wide fund to provide extra funding for public spaces and high streets.

The UK government announced £214m in new funding in Wales, including £35m for Wales’ 22 local authorities to use over the next two years.

It said nine authorities – including Caerphilly – would receive up to £20m each.

Sir Keir was asked by BBC Wales if he would go to Caerphilly: “I don’t know whether I’m going to Caerphilly. It’s obviously coming up very soon and we’ve got our party conference next week.”

When it was put to him that it was a key by-election, Sir Keir added: “As you know, we’re in Liverpool next week, we’ve got a big party conference coming up.”

Asked if he was an electoral asset there, he added: “I work very well with the first minister, and as long as we keep championing the difference we’re making, that’s what matters.

“Even today in Caerphilly, we’ve announced our Pride in Place fund, which is ten years worth of funding into Caerphilly, and control locally of what that money is spent on.”

Recent opinion polling have suggested Labour is in third place in Wales for the next Senedd election in May, with a recent YouGov survey putting the party on 14%.

Asked if he was worried about being the first Labour leader to lose Wales, he said: “Well we’ve got a long way to go into those elections.

“The most important thing is to be absolutely clear of the huge benefits of having a Labour first minister and a Labour prime minister working together.”

He said the UK government had provided “a record settlement for Wales, the biggest since devolution”, referring to funding for the Welsh government. He said Labour had invested in fixing coal tips, in the railways, in renewable energy and Port Talbot.

When the recent opinion poll was put to him, Sir Keir said: “We have to work hard, we have to earn every vote.

“We did very well in the general election last year. So we’ve shown what we can do.”

Senior Labour figures have recently painted a bleak picture for the party next May, with one suggesting Labour was facing the “biggest kicking” in its history.

By Gareth Lewis, Wales political editor

Labour are up against it in Caerphilly in next month’s by-election – a previously safe seat for the party – and you might think a bit of personal door-knocking would be a priority for a PM already looking at dire polling for next year’s Senedd election.

Polls also suggest that Sir Keir is not a popular prime minister and he didn’t directly address whether he thought he would be an electoral asset there.

As for next May his pledge to “earn every vote” is the sort of thing you would expect a politician to say.

But it’s perhaps a tacit acknowledgment that Labour really do have to fight to stay in power after more than a century of hoovering up votes and domination in Welsh politics.

Sir Keir was on home turf for these traditional pre-conference interviews on a skyscraper looming over north London, but his problems lie further afield.

On Thursday the UK government announced the Pride in Place programme will see nine further councils receive £20m each over a decade.

They are:

• Blaenau Gwent
• Neath Port Talbot
• Newport
• Rhondda Cynon Taf
• Caerphilly
• Carmarthenshire
• Conwy
• Cardiff
• Swansea

A total of £1.5m would be made available to each of Wales’ 22 local authorities to spend over two years, except Bridgend which will get £3m.

The scheme is similar to the previous levelling up fund, in that councils have to make bids to the UK government for the cash.

Sir Keir said: “This is a huge investment, but what matters most is who decides how it’s spent: the neighbours, volunteers and parents who know their communities best – the people with real skin in the game.”

Candidates announced so far for the Caerphilly Senedd by-election are:

• Conservatives – Gareth Potter
• Gwlad – Anthony Cook
• Labour – Richard Tunnicliffe
• Plaid Cymru – Lindsay Whittle
• Reform UK – Llŷr Powell
• Welsh Liberal Democrats – Steve Aicheler
• Greens – Gareth Hughes