As National Grid calls for more energy, is Britain's old, creaking system failing?

National Grid today issued a call for more energy, as mild weather receded along with our national power reserves.

This is an unusual measure, which last happened in 2012. What some may find worrying is that it has occurred so early into the cold season.

It is being blamed on "multiple breakdowns" at UK power plants.

National Grid says predicted reserves will be lowest between 4.30pm and 6.30pm this evening, and that's when they want more energy.

Britain's background shortage of energy generation has increased the risk of blackouts.

National Grid has new emergency powers to keep the lights on over winter. It can now pay big industrial users, such as factories, to switch off. It could also use mothballed power plants.

Such measures are a last resort. First comes the request for extra generation, as has happened this afternoon.

Read: Power firms 'must boost output after plant breakdowns'

Experts tell me that the end of October and start of November has long been seen as an energy "pinch point" because some generators are still undergoing pre-winter maintenance.

Signs of the end of mild weather and the breakdowns at some plants have intensified the problem.

National Grid says there is no immediate risk of power shortages and "for commercial reasons", it will not identify which plants have suffered breakdowns.

The call for extra energy triggers a response from the power generators who should sell more through the usual market to top-up reserves.

In some ways, this shows the system is working - but on the other hand, it shows the system is not working well enough, as it is not producing sufficient reserve energy.

If this happens on a regular basis it will be seen as a sign that an old and creaking system is failing.