LONDON (Reuters) - The delicate threads that hold modern life together are dramatically cut by an unexpected threat from outer space, with disastrous effects.

It's the stuff of science fiction usually associated with tales of rogue asteroids on a collision course with earth.

But over the next two years, as the sun reaches a peak in its 10-year activity cycle, scientists say there is a heightened risk that a whopping solar storm could knock out the power grids, satellites and communications on which we all rely.

"Governments are taking it very seriously," says Mike Hapgood, aspace weather specialist at the Rutherford Appleton Laboratory in the UK. "These things may be very rare but when they happen, the consequences can be catastrophic."

Hapgood said that solar storms are increasingly being put on the national risk registers used for disaster planning, alongside other rare but devastating events like tsunamis and volcanic eruptions.

The statistics support this, he said. There is a roughly 12 percent chance of a major solar storm every decade, making them a one-in-a-hundred-year event. The last major one was over 150 years ago.

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The threat comes from the magnetically-charged plasma which the sun belches out in so-called coronal mass ejections. Like vast bubbles bursting off the sun's surface, they send millions of tonnes of gas racing through space that can engulf the earth with as little as one to three days warning.

The geomagnetic storms they stoke can induce strong currents in national power grids that literally melt the expensive transformers that form the cornerstones of the system.