The chairman of Britain's private healthcare giant Bupa is the latest business leader to back a 'No' vote in the looming Scottish independence referendum.

Lord Leitch is known to be one of the most prominent signatories of a letter from business people backing the Better Together campaign, a source at which confirmed reports his name was on the document to be released shortly. There are thought to be around 130 signatories in all.

A Bupa spokeswoman said Leitch was giving his own personal view and not that of the company, adding: "Bupa is apolitical – we work constructively with governments of all parties."

No campaigners will see the backing of Leitch, who has also been deputy chairman of Lloyds Banking Group, as a coup in the final days before the crunch vote on 18 September. Polls suggest there is nothing to split the two sides of the debate, though a significant chunk of voters are undecided.

Some businesses have raised concern about the possibility of independence. The Royal Bank of Scotland (RBS), which is headquartered in Edinburgh, said independence would have a negative effect on its business.

And insurer Standard Life has drawn up plans to move south of the border if the Yes campaign is triumphant.

This is because of the uncertainty around what independence would look like for Scotland. There are still unanswered questions around what currency would be used, how the regulatory system would be built, and if Scotland would be a member of the European Union (EU).

The leaders of the three main Westminster parties – the Conservatives' David Cameron, Labour's Ed Miliband and the Liberal Democrats' Nick Clegg – have all rushed to Scotland in a last ditch bid to convince voters against breaking up the UK.