The future of HSBC’s headquarters in Canary Wharf has exploded into a major political row two weeks before the general election.

The bank had already signalled it was disturbed by the level of regulation on its UK-based assets but has now escalated its concerns with a pointed attack about the country’s role in the EU.

The Conservatives have pledged to hold an in/out referendum on the subject if it were to win another term, sowing seeds of uncertainty among big businesses about the future direction of trading relations.

Labour, normally a foe of the big banks with extensive plans to bring them to heel, have seized upon HSBC’s concerns.

In a statement HSBC chairman Douglas Flint said: “One economic uncertainty stands out, that of continuing UK membership of the EU.

“In February we published a major research study which concluded that working to complete the Single Market in services and reforming the EU to make it more competitive were far less risky than going it alone, given the importance of EU markets to British trade.”

In a speech this morning, Labour leader Ed Miliband said the referendum posed “a threat” to this stability.

He said: I’ve got to be candid, and we have seen it confirmed again with HSBC today, I think all of this poses a grave risk to Britain’s position in the world. Of course the European Union needs to change, there are demands for it to change in almost every other member state.”

Danny Alexander, the Lib Dem chief secretary to the Treasury, said: “Today’s HSBC announcement confirms fears that businesses have over a swing to the right and the prospect of a ‘Blukip’ coalition pulling us out Europe.

“David Cameron, held hostage by Ukip partners and the right wing of his party, would drive the country further towards a ‘Brexit’ – which would hit both jobs and business.”

In response, the Prime Minister David Cameron sidestepped the HSBC question but said: “London is the world’s leading financial centre, has improved as a financial centre not least by changing the way we regulate banks so that we wouldn’t have to bail them out with taxpayers’ money in future as the last Labour government had to do.

“But it is an important reminder of how vital it is that we keep a pro-enterprise, pro-business, pro-employment policy in our country.

“We need to keep taxes low, make this an attractive place to invest. All the time I have been prime minister that is what we have been doing, record levels of inward investment coming here.”