The volume of the remaining North Sea oil reserves could exceed current estimates by around 20 per cent, geological experts have claimed.

With some 37 billion barrels having already been extracted from the UK Continental Shelf (UKCS) since oil was discovered there, it had been widely believed that there are as much as 25.5 billion barrels-worth still to be recovered in the region.

However, in a new BBC report, geologists working with the oil industry have stated that they believe this figure to be closer to 30 billion and, with the recent advances made in extraction technology and the current rapid upward trend of oil prices, reserves which had hitherto been ignored are now economically viable.

Despite this, operations around the UKCS still face tough competition for investment from a number of cheaper locations around the world and Oil & Gas UK has argued that more needs to be done to attract further funding.

Mike Tholen, economics director at the industry body, told the Times: "Oil & Gas UK currently estimates that up to 26 billion barrels of oil and gas remain to be recovered from the North Sea but none of these volumes will be easy to recover.

"Securing investment to develop and extract them relies on international investors perceiving the UK as a competitive place to do business."

According to the latest industry figures, investment in the UKSC fell by around £1 billion to £4.9 billion over the course of 2007.