Just two years ago, at his 2011 Budget, George Osborne opted to take another £2bn in taxes from producers, adding to earlier changes by Labour that were already damaging investment and confidence.

The industry responded in an all too familiar way by cutting budgets and putting investment on hold. Over the last two years production has slumped 30pc, exploration drilling has tailed off sharply and the Treasury’s tax take has dropped 35pc to £7.4bn.

It might not all have been down to the Chancellor but the damage was sufficient to push him into performing something of a U-turn. After talks with the industry trade body Oil & Gas UK, new incentives and tax allowances were unveiled to bolster confidence and investment.

The Chancellor receives a substantial down payment on that decision today with the annual survey from Oil & Gas UK disclosing that North Sea investment this year will be the biggest and most extensive for 30 years. Spending is forecast to be at least £13bn, but with operating costs expected to be running at £8.5bn and development costs per barrel five times higher than a decade ago, companies say there is little room for investment mistakes.

Producers say they are ready to embark on the biggest exploration programme for six years. Reserves in existing fields or under development are also at their highest level since 2007 at 7.4bn barrels, adding to the growing belief that Britain will still be an oil producing nation through to 2040-50.

In total, the survey claims, companies plan to spend almost £100bn in the next few years. They are already committed to spending £44bn, and Malcolm Webb, chief executive of Oil & Gas UK, says there is more than a 50pc chance that another £30bn will be approved.

Production is forecast to rise by a third to 2m barrels of oil and gas a day by 2017, although by then it will be only back to the 2010 level. Forecasts suggest production this year could be down to 1.45m-1.5m barrels a day.

Mr Webb says that projects approved in the last two years alone will generate £100bn for the economy, create thousands of jobs and provide an additional £25bn for the Exchequer in production taxes.

In the last six months companies have announced investments worth more than £8bn, creating around 6,000 new jobs. Licence conditions are contributing to a surge in exploration with 130 wells planned over the next three years to help replace the fall of 500m barrels in company reserves because new discoveries failed to keep pace with production.

The Chancellor would have liked the windfall earlier with an election two years away and growth in the economy proving elusive. The industry is anxious to demonstrate that companies and investors are responding to the incentives and Government drive to squeeze more out of the North Sea.

For Alex Salmond, the first minister of Scotland, the bullish assessment will raise the profile and importance of North Sea oil and gas in the independence debate and provide him with more economic leverage by insisting that “it’s Scotland’s oil”.

The political dimension has been bubbling below the surface but the fresh lease of life projected in today’s analysis provides a considerable boost for supply companies north and south of the border and the 440,000 workers, most of them in Scotland, contributing to the industry.

In oil industry parlance the North Sea is a mature province, developed rapidly to produce the maximum benefits for the economy and balance of payments. Oil production peaked in 1999, fewer than 30 years after the first big discoveries and has been falling sharply as investors lost confidence when confronted by a more aggressive tax regime and rising costs.

The arrival of new companies and a series of asset sales has stimulated fresh exploration in some of the older fields and increased recoverable reserves. Fifty new field developments are included in the latest programme, eight of them west of Shetland, 23 in the central North Sea area and six in the southern North Sea or Irish Sea.

Most of them are small with recoverable reserves of under 20m barrels, while 11 could yield more than 100m. Over the last year the Energy Department has approved 33 projects involving investment of £13.4bn.

There is a sting in the survey tail. Companies estimate they face a bill of around £35bn by 2040 to shut down and dismantle installations on exhausted fields. They have asked for help. Mr Osborne will oblige in this year’s Finance Bill with tax relief.