LONDON, May 4 (Xinhua) -- Britain's ruling Labour Party is facing a key local election test, as pressure builds on Prime Minister Keir Starmer over a disputed diplomatic appointment, weak polling numbers and opposition attacks, raising questions about the party's unity, leadership authority and ability to sustain public confidence.

Last week, the House of Commons voted down an opposition motion seeking to refer Starmer to the Commons Privileges Committee over claims he misled the parliament regarding the vetting of former British Ambassador to the United States Peter Mandelson.

On Tuesday, lawmakers voted 335-223 against the motion, meaning the prime minister will not face a formal inquiry. However, 15 Labour Members of Parliament (MPs) backed the call for an investigation, despite the party's large majority in parliament.

During Prime Minister's Questions on Wednesday, Conservative Party leader Kemi Badenoch said Starmer was trying to "save his own skin" in the previous day's vote and linked the Mandelson controversy to wider questions over welfare, defence spending and economic management. Liberal Democrat leader Ed Davey and Scottish National Party's Westminster leader Stephen Flynn also used the session to question Starmer's judgment and political authority.

The dispute centers on Mandelson's appointment as ambassador. British media reported earlier this month that Mandelson had failed a security vetting process after his appointment, but the Foreign Office later overruled this decision, granting him clearance to take up the post.

Starmer told parliament he had not applied pressure in the appointment process and said the procedure had been proper. Opposition parties accused him of misleading parliament and questioned his judgment.

The vote came at a sensitive moment for Labour, with local and regional elections due to take place on Thursday. Analysts said the opposition's pressure on Starmer should be seen not only as an attempt to pursue the Mandelson case, but also as a political move to weaken Labour before the elections.

Jonathan Sullivan, a political scientist at the University of Nottingham, told Xinhua that Starmer is "hanging on by a thread," and that the Mandelson affair has "crystallized" several existing criticisms of Starmer, especially the perception that he is not fully in control of his government.

"If Labour performs poorly in the May local elections, Starmer could be in jeopardy," Sullivan said.

The Conservatives have sought to frame the case as a question of standards and consistency. They pointed to Starmer's own role as opposition leader in 2022, when he pushed for an investigation into then-Prime Minister Boris Johnson over whether he had misled parliament during the "partygate" scandal. That inquiry later contributed to Johnson's downfall as prime minister and his resignation as an MP.

However, experts said the current crisis is also different. Starmer still commands a large parliamentary majority, and there is no clear consensus within Labour on who should replace him if his position weakens further.

Iain Begg, a professor at the London School of Economics and Political Science, told Xinhua that pressure from both political opponents and Labour's own side is growing and that the controversy has weakened Starmer's authority, which had already been damaged by policy U-turns and hesitation on domestic issues.

Begg said the Mandelson affair "could well be the straw that breaks the camel's back," but Starmer is partly being kept in place because none of his potential successors has strong enough backing.

This means the May elections may not be a simple referendum on Starmer personally, Begg said, but rather a test of Labour as a whole. A poor result could worsen an already difficult situation for the governing party, he noted.

Polls have shown Labour under pressure before the local elections. The latest YouGov voting intention survey, conducted on April 26-27, put Reform UK in the lead at 26 percent, followed by the Conservatives at 19 percent and Labour at 18 percent, with the Greens at 15 percent and the Liberal Democrats at 13 percent.

YouGov said the figures were broadly within the margin of error of the previous week, but Labour remained well behind Reform UK. Separate local election projections have also pointed to possible heavy Labour losses, with Reform UK and the Greens expected to make gains in several areas.

John Bryson, a professor at the University of Birmingham, said the controversy raises broader questions about Starmer's judgment and the way the appointment was handled.

"The decision to appoint Mandelson must have been discussed and approved by the Cabinet," Bryson told Xinhua. "This is not just Starmer's problem but a cabinet problem, and thus a much broader Labour Party problem."

Whether Starmer's position becomes untenable may depend on what happens next, including any further reporting or official clarification on the appointment process, Bryson said. But he argued that the issue has already moved beyond a short-term media cycle.

The Institute for Government, a London-based think tank, said the Mandelson row also showed how parliamentary scrutiny could become more difficult for governments to contain in a more fragmented political environment.

"The increasingly fragmented nature of parliamentary politics -- particularly the development of strong groupings within parties willing to diverge from their leadership in parliament -- makes it more possible for governments to be subjected to these procedural mechanisms despite having a parliamentary majority," wrote Hannah White, the institute's director.