RBS boss Stephen Hester said last week that his bank was opening thousands of new customer accounts but failed to say that is was paying $220 – £120 – to every new customer as a sweetener in 12 American states.

“UK taxpayers and RBS savers in Britain will be outraged by this kind of marketing activity.

“In the week when every one of us is giving an extra £500 per person to RBS to keep it afloat, it’s a slap in the face to existing UK savers who are getting extremely poor returns,” said Matthew Elliott, the chief executive of the Taxpayers’ Alliance.”

“The idea that Americans are being super gold-plated, when customers in the UK are propping up the state-owned RBS, is rather insulting and needs to be addressed,” he added.

Citizens Bank and Charter One Bank, which are both owned by RBS, say they have opened a record number of new accounts with its gift offering, which runs until November 13.

Citizens Bank has even opened a branch in a Dunkin Donuts outlet and is offering free coffee for a month.

RBS needed a £25.5billion injection of UK taxpayers’ money last week, with an immediate requirement of £13bn to keep it afloat.

Yet the Citizens Financial Group, based in Rhode Island, is giving away cash to induce new customers, including a $1,000 (£600) gift to savers wanting a new home loan.

RBS last week revealed plans to cut 3,700 jobs – and the Chancellor Alistair Darling announced the disposal of assets including branches and insurance companies.

Many of RBS’s deep-rooted problems stem from investments made in the American home loan market, including its purchase of ABN Amro, which had massive toxic assets in the US.

RBS Securities, formerly known as Greenwich Capital Markets, is a wholly owned subsidiary of Royal Bank of Scotland Group and operates in the United States. It is engaged in the purchase, sale and financing of US Treasury bonds and mortgage-backed securities.

Both RBS and HBOS in the UK were involved in a “golden hello” battle before the credit crunch.

Critics said that this kind of marketing for new customers can be expensive and short-term as customers sign up, take the money and then close the account soon after.

Professor Stewart Hamilton, the Scots-born dean of the Faculty of Finance at IMD business school in Lausanne, said: “The questions that really need to be asked here are, what is the cost of setting up these accounts; what’s the likely retention rates and what are the perceived benefits? It might well be an economically sound thing to do.”

He said banks have been wooing customer with introductory offers for years, but in this case it is a politically sensitive matter.

“With RBS owned 86% by the UK taxpayers, the political sensitivity of paying for customers in America should have been considered before the business case.

“If Stephen Hester did not announce this method of growing customers accounts to the City, then that’s an issue too.”

Martin Bischoff, the head of Citizens Bank’s Consumer and Business banking, said: “Our recent offers have enabled us to attract tens of thousands of new Citizens Bank and Charter One customers.

“As part of our focus on exceptional service, we look forward to providing our customers with banking solutions to achieve their financial goals.”

A UK Treasury spokesman said: “We do not comment on the operating and marketing decisions of banks.”