The UK chief executive of the German manufacturing group Siemens has said Brexit is making Britain an international “laughing stock”, while urging MPs to pursue a softer withdrawal from the EU.

Jürgen Maier said Britain was wrecking its reputation for business stability, putting investment in the country at risk and threatening the economy. A no-deal Brexit would inflict further damage, he said, while urging MPs to reach a consensus and back a customs union with the EU.

Writing an open letter to MPs published by the Politico website, he said: “The world is watching, and where the UK used to be beacon for stability, we are now becoming a laughing stock.

EasyJet issues Brexit warning, as crisis turns UK into 'laughing stock' - business live Read more

“Enough is enough. We are all running out of patience. Make a decision and unite around a customs union compromise that delivers economic security and stability.”

The head of Siemens UK, which is one of the country’s biggest industrial firms with annual revenues of £5bn and 15,000 staff, said political turmoil over Brexit was making it harder for him to win support for British investment from the firm’s managing board in Germany.

The warning came after official figures showed business investment slumped last year, declining in every quarter for the first time since the last recession in 2008, as companies put spending decisions on hold due to the lack of clarity over the UK’s future trading relationship with the EU.

Business leaders have become increasingly exasperated with MPs’ inability to break the deadlock over Brexit in parliament, reacting with frustration after Theresa May’s plan was defeated for a third time on Friday.

Maier has previously said Siemens UK was ramping up stocks of critical supplies because of Brexit, stocking more components required for machines used to keep the country running, including on infrastructure such as railways and food processing.

The Anglo-Austrian businessman has developed a reputation in recent years as one of the most outspoken captains of industry in Britain, debating politics on television programmes such as Question Time when other business leaders would shy away.

Sign up to the daily Business Today email or follow Guardian Business on Twitter at @BusinessDesk

He campaigned for remain before the EU referendum but backed the prime minister’s deal, saying it would provide certainty for businesses and avoid the UK crashing out without an agreement. However, he said the current approach had failed and called on the government to compromise with MPs.

He said he believed a majority would most likely be found through a UK-EU customs union, which was among the options closest to winning support last week when MPs voted on eight separate proposals for breaking the impasse.

Such an outcome would enable the continuation of frictionless trade with the EU and save businesses billions of pounds every year on unproductive customs declarations, he said.