Bob Dudley, the head of oil multinational BP, has become the most high profile businessman so far to speak out against the idea of independence for Scotland, voicing concerns over the economic consequence and saying there are 'big uncertainties' surrounding a separate Scotland currency and membership of the EU.

In a BBC interview, Dudley said 'all businesses' are worried about the impact of a Scottish separation and that Scottish independence represented a 'question mark' for BP which plans to invest £10bn in the North Sea between 2011 and 2016, its highest ever investment in the region.

Dudley said that an independent Scotland would create extra costs for BP because of the need for duplicate centres, while he also had concerns over the tax regime as well as the currency. He stated: 'Great Britain is great and it ought to stay together.'

Alistair Darling, head of the Better Together campaign which opposes an independent Scotland, said Dudley's comments marked the biggest intervention by a major business so far in the referendum debate.

'I hope that more companies and business leaders speak out over the coming weeks and months. This debate is far too important to be left to politicians alone,' Darling said.

However, a spokesman for the pro-independence Yes Scotland campaign said: 'With independence, the continued use of sterling has the overwhelming support of the people of Scotland and the public in the rest of the UK.'

This view has been challenged by Chancellor George Osborne who said a currency union based on the pound would be 'unworkable', based on analysis by the Bank of England governor Mark Carney which suggested Scotland and England would find it very difficult to agree public sector spending limits and a banking union if the vote for independence went through.

Earlier this week ICAS highlighted unresolved questions about the future of Scottish pension provision if independence gets the go ahead, saying there were issues about how UK-wide cross-border schemes would be financed and managed. The institute said this was a particular challenge given the ageing demographic profile in Scotland and a commitment to providing higher pensions post independence.