Oil giant Shell drilled into the Scottish independence debate yesterday, claiming that a split would hit the "certainty" of its North Sea profits.

North Sea oil and gas reserves have taken centre stage, with SNP ministers promising to create a national oil fund to serve as an independent Scotland's economic base while critics point to industry predictions of declining revenues.

Scottish First Minister Alex Salmond has also ruled out any tax increases on oil and gas firms and guaranteed tax relief on decommissioning rigs, pledging "stability and predictability" for the industry.