A year or so ago, the oil and gas sector was supporting 440,000 jobs across the United Kingdom.

According to the Scottish Government's estimate, 45 per cent of those jobs, fully 196,000, were in Scotland. There have been ups and downs since but the hard fact remains: the North Sea is of vast importance on both sides of the Border.

The fact lends perspective to any celebrations over the collapse in oil prices in recent months. The slide in Brent crude to the $50 a barrel mark might still cause a few to crow over dashed dreams of an independent Scotland. Since independence did not happen, it hardly matters. What is happening to oil prices now is happening in a UK that needs all the revenue it can get.

Lower prices might meanwhile help us all to fill our cars and heat our homes more cheaply. No one will reject those gifts. If warnings to industry from the Chancellor, George Osborne, are to be believed, the collapse should also lead to cheaper prices for all utilities, to more manageable food bills as transport charges fall, and to lower costs all round. Again, these are reasons to be cheerful.

Already, however, the North Sea's older fields are at the point of ceasing to be viable. Worse, incentives to invest are evaporating. The oil and gas to which the UK can lay claim were challenging development prospects before prices began to fall. With every cancelled project, jobs and potential revenue are forfeit. Scotland, in particular, might be about to learn that silver linings have dark clouds attached.

The same could be said of the wider world. No oil producing country has reason to be cheered by a $50 barrel price. For some, such as Russia and Iran, it is catastrophic. Even the United States, so recently boasting of energy independence, is learning that shale and "tight oil" fracking are not panaceas when the price falls below $80. Saudi Arabia needs $104 a barrel to balance its budget. Stock market jitters tell the tale: the fear now is of global instability.

There is another story: there is supply, but precious little demand. On most estimates, producers are pumping two billion barrels a day more than the market needs. The global economy is shrinking, not growing. Scotland's big, impending North Sea problem might seem like a drop in the ocean before long.