FIRMS are facing a multibillion-pound pensions timebomb under EU rules that would kick in if Scotland voted to become independent, the country's accountants warn today.

Employers would be forced to plug gaping holes in exposed pension schemes immediately as underfunded "cross-border" schemes are not allowed under the EU's Pensions Directive.

The requirement could bankrupt some companies, accountants fear, forcing their schemes to collapse and leaving hundreds of thousands of past and present workers seeking help from state-backed protection funds.

In a robust response, the Scottish Government said there was no reason why an independent Scotland could not follow the example of the UK's existing agreement with Ireland to cover such pension issues.

The warning comes in a report published today from the Institute of Chartered Accountants of Scotland (ICAS).

The body makes an urgent plea for the Scottish and UK governments to begin talks to resolve a list of potential pension difficulties if Scotland becomes independent.

Most occupational pension schemes do not have the funds to cover their liabilities. Many are implementing recovery plans over the next decade and a half to rebuild their assets and bring them closer into line with payments due now and in the future.

The arrangements are permitted within a single country, but pension schemes operating in Scotland and south of the Border would be classed as "cross-border" if Scots vote Yes in the poll on September 18, 2014.

The ICAS report warns that under EU rules "pension liabilities would have to be fully funded at all times and underfunding would have to be rectified immediately rather than through a staged recovery plan".

It said the regulations "would have major cost and cash-flow implications for employers" and the continued solvency of defined benefit schemes would depend on firms' ability to find extra funding straight away.

An independent Scottish Government could seek an exemption from Brussels or a "period of grace" to plug the gaps, it added. However, the study casts doubt on whether firms would be granted longer than 10 years to do so.

ICAS suggests occupational pension schemes could be split into Scottish and UK funds, but asks: "Is there a mechanism for splitting schemes and, if so, what are the risks to scheme members of doing so?"

The report also highlights the need for complex talks to establish responsibility for state and public sector pensions – which are currently underfunded to the tune of £60bn in Scotland – after independence.

ICAS believes an independent Scotland would eventually need its own version of the Pension Protection Fund, the Government-backed scheme which ensures workers who lose their occupational pensions receive a portion of their retirement cash.

David Wood, ICAS executive director of technical policy, said: "For schemes in the private sector, which became cross-border schemes in the event of independence, addressing any underfunding would be a priority for both Scottish and rest of the UK employers.

"ICAS calls on the Scottish and UK Governments to engage with business, the pensions industry and the EU to minimise the financial impact on these schemes, their sponsoring employers and the people who have paid into the schemes.

He called on both governments to engage with citizens and other pension stakeholders to prepare a way forward, and agree transitional arrangements, on the issue.

Shadow pensions minister Gregg McClymont said: "The introduction of the requirement of cross-border schemes to be fully funded has not been addressed. There needs to be clarity on this issue ahead of the referendum."

Scots Tory finance spokesman Gavin Brown said: "The industry itself could have to find substantial sums to top up pension funds because of the rules of operating cross-border schemes. This could have obvious knock-on effects for business and the premiums paid by customers."

Scottish Liberal Democrat leader Willie Rennie MSP added: "The issue of EU legislation on pension schemes operating between Scotland and the rest of the UK is a legal quagmire which can only be achieved with independence."

David Lonsdale, assistant director of CBI Scotland, said: "There are significant gaps in knowledge about what Scottish independence would mean for pensions and personal savings."

A Scotland Office spokesman said the cross-border directive would have major implications for employers and pensions firms on both sides of the Border.

A Scottish Government spokesman said: "We welcome this contribution to the debate from ICAS and look forward to further engagement with them and the pensions industry.

"The cross-border management of pensions is commonplace throughout the EU, as underlined by the fact the UK has already introduced measures for cross-border schemes with Ireland. There is no reason why similar arrangements cannot be put in place for an independent Scotland."