Jim Lovell, of the British Geological Survey, says people were shaken in their beds

The tremor, which had its epicentre two and a half miles (4km) south of the Isle of Arran, was the biggest in Scotland since 1927.

But seismologists say there is no reason for people to worry as earthquakes are actually becoming less frequent.

Around 00.15GMT police received calls from a number of residents in Lamlash on the Isle of Arran and as far away as Kilmarnock and Saltcoats on the mainland.

People reported being shaken from their sleep and said buildings physically shook while others said they heard a noise which sounded like an explosion.

Offshore epicentre

Seismologists at the British Geological Survey (BGS) in Edinburgh confirmed an earthquake registering as a magnitude four. It emanated from a point 19km under the Firth of Clyde, as did a 1.6 after-shock which was felt 14 minutes later.

There have been no reports of any injuries or structural damages but the tremor was felt as far away as Peebles, 120km (80 miles) away.

BGS seismologist Maureen Ritchie said the quake did not compare with the 1984 Lleyn Peninsula incident.

Although it was the UK's deepest ever earthquake it caused widespread damage on the lightly-populated peninsula in North Wales and was felt as far away as Liverpool.

Worse than that though was the 1931 Dogger Bank quake, which had its epicentre offshore but caused serious damage to the East Anglian coast.

Ms Ritchie said: "Because we have more instrumentation than ever before we are picking up more seismic activity than in the past but events are smaller."

Regular events

The UK has between 200 and 300 seismic "events" every year but few cause damage.

Ms Ritchie says the British Isles is relatively aseismic - in other words devoid of earthquake activity - because it is a long way from the nearest tectonic plate.

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"The nearest is the Mid-Atlantic Ridge, which runs right through Iceland, but that is a long way away," she said.

Japan is the world's most seismically active region - although China has suffered more earthquake deaths this century because of its high population density - while Greece is the most active region in Europe.

Ms Ritchie said the west coast of the UK is more susceptible to quakes than the rest.

"Part of the reason may be the fact that the North West of Scotland is believed to be rebounding since the last Ice Age and that is adding pressure," she said.

Ms Ritchie said while the UK is a relatively calm region geologically there is no reason for complacency.

'Potential for damage'

"Had an event, like the Dogger Bank event of 1931, occurred under a city like Liverpool it would have caused a lot of damage," she said.

Suzanne Moore, of the Association of British Insurers, said most household insurance policies cover the holder against earthquake damage.

She told BBC News Online: "In this country the risk of an earthquake is pretty remote and there is not a material difference between the risk of living in Scotland and Cornwall."

But she said quakes were taken into account by insurers abroad, especially in California and Japan, where premiums tend to be much higher than in the UK.