John Healey’s Budget has assumed the government will approve North Sea discovery drilling projects that produce in excess of a billion barrels of oil and gas, in the clearest sign yet that ministers plan to rubber-stamp a wave of new drilling after Jackdaw and Rosebank. In its scorecard for the Chancellor’s maiden fiscal event, the Office for Budget Responsibility accounted for a boost in tax receipts from the “development of new fields” that not only include the controversial Rosebank oil field but also other “future…