The "remain" camp held a 15-point lead over its "leave" rivals in Britain's EU referendum campaign, according to the latest poll from ORB for the Telegraph newspaper, published on Monday.

The poll found that among all respondents, support for remaining in the union stood at 55 per cent, while that for the so-called Brexit option was at 40 per cent.

Britons will vote on June 23 on whether their country should remain in or leave the 28-member bloc.

The "remain" camp held an eight-point lead over its "leave" rivals in a separate ICM poll for the Guardian newspaper, also published on Monday.

The poll was reported as some US banks said a Brexit could result in them giving up parts of their business in the EU altogether.

The option is an extreme scenario under consideration by some Wall Street firms if the terms of an exit, currently a matter of speculation, leave financial services companies in Britain unable under their current set-ups to do business inside the EU, according to discussions Reuters had with several US banks and their lawyers.

The scenarios being studied by taskforces at US banks underscore the extent to which the London operations of non-European banks are linked to business on the continent.

In particular focus are the banks' market operations, as trading of most European securities is regulated at the EU level but conducted by many investment banks mainly out of London.

The five largest US banks employ 40,000 people in London, more than in the rest of Europe combined, taking advantage of the EU "passporting" regime that allows them to offer services across the bloc out of their British hubs.

Having to reorganise business in order to set up new continental European outposts – which US banks say is a worst-case scenario that they are being forced to consider – would be so costly that it would make some rethink their commitment to the bloc altogether.

"The costs may lead some banking groups to reassess how important Europe is in the context of their global business and what sort of presence they wish to maintain post-Brexit," said Edward Chan, a partner at the law firm Linklaters, which has been advising banks on contingency arrangements.