PROPOSED changes to employer taxation could threaten future investment by the oil and gas industry, according to business ­advisers BDO.

HM Revenue & Customs is planning legislation next April which will challenge the use of offshore intermediaries to keep employees off the payroll.This will threaten some companies with a "significant bill for income tax and national insurance contributions", BDO says.

"At present the UK oil and gas sector arguably enjoys a 13.8% tax advantage as no employer's NIC is being paid. But this could end next spring as the Government cracks down on tax loopholes," the adviser adds.

BDO notes that while the North Sea sector has been booming, it is sensitive to oil prices and to any change in financial viability.

Brian Lovie, director of employment taxes with BDO, said: "Although the proposals could impact any UK business using employment agencies or outsourcing services involving UK-resident employees where an offshore intermediary is involved, the oil and gas industry is expected to be a major target for HMRC."

He went on: "A dip in oil price, or new technologies such as fracking, which can offer greater flexibility and increased profitability, may make the oil and gas ­exploration companies think again about the viability of the North Sea if they have to add 13.8% to their UK employment costs.

"It is worth at least considering whether the potential increase in tax revenue for the Treasury from this latest challenge to perceived UK tax avoidance will be worth it if companies reduce their investment in the sector."

A survey of oil and gas executives by Ernst & Young published this week found 79% expect that a "yes" vote in the independence referendum would lead to higher taxes on the industry.

More than half of the business leaders supported lowering corporate tax rates to stimulate investment.