John Gell will be staring nervously at the sky tomorrow night. He is no star-watcher, but a rare event in the heavens could visit disaster on his home and those of thousands of others who share his predicament.
One of the highest tides ever seen in Britain threatens to be the sternest test the country's sea defences will see for 100 years. As the Moon's orbit swings it close to Earth and into a perfect alignment with the Sun - a phenomenon known as the autumn equinox - a huge surge in gravitational pull will draw tides up to alarming levels. Billions of tonnes of water will be on the move.
If the high tide coincides with bad weather tomorrow night, the floods will be devastating. 'If the weather turns bad, we're in trouble,' Gell said last week as he peered from his beachfront cottage at Pevensey Bay in East Sussex.
Gell's concerns will be mirrored in the million British homes that have been identified as vulnerable to coastal flooding. A dramatic deterioration in the weather during the next 24 hours could lead to the sea overwhelming coastal defences.
The Environment Agency confirmed last night that measures for dealing with a mass evacuation have been put in place. Local authorities have stockpiled sandbags, while emergency services are on standby.
The homes of more than 1.1m people - worth £120 billion - are at risk from the sea. Most vulnerable, however, are the 50,000 homes on the south coast, where this week's tide is forecast to be highest.
Peter Midgely, flood defence manager for southern England, said: 'The juxtaposition of the Moon and Sun is exerting their maximum influence on the Earth and consequently the tide.'
The tide has increased profoundly over the past few days, reaching 5.3m off Sussex on Tuesday and is forecast to peak at 8.2m. Attention is now focused on the weather. The emergency services and the Met Office will remain in regular contact throughout today.
If it stays unseasonally stable - as predicted - the Environment Agency is confident there will be no serious flooding. A spokesman for the UK Hydrographic Office in Taunton said: 'Fortunately the exceptionally high tide is not likely to be accompanied by bad weather.'
However, a sudden drop in pressure could trigger a 'storm surge', while strong onshore winds could add two metres to the tide's height, with potentially disastrous consequences. Wind strength - and direction - are key. A powerful south-westerly could pose problems for the south coast while northerly gusts could drive the high tide on to the coastline of Norfolk and the Thames estuary.
A combination of high tide and strong winds was blamed for the infamous floods of 1953, which claimed the lives of more than 300 people from Scotland to Essex. Although London narrowly escaped, the government embarked on measures to protect the capital leading to the construction of the Thames Barrier at Woolwich in 1965.
Occasionally, though, the sea has breached coastal defences with the residents of Pevensey Bay among those accustomed to severe flooding. Almost three years ago, water burst through the resort's shingle barrier and inundated bungalows situated in marshland.
Locals are horrified at the prospect of a repeat. Lynne Ware, proprietor of the Pevensey Bay Aqua Club, was fortunate then: a makeshift barricade of beer barrels and felt covering stopped water entering the bar. Then weeks later, police issued an evacuation order on Christmas Eve as a raging tide once again threatened the resort. Again Lynne escaped. She will spend today monitoring the skies for a shift in the weather. 'If the skies changes, then I'll take action,' she said.
John Gell, a 66-year-old former fisherman, knows only too well what can happen. A storm in the 1950s destroyed the wooden frontage of his home. So much water gushed inside that he was forced to smash apart the rear wall with a hammer to drain it.
Some coastal areas have exacerbated the impact of flooding by building in vulnerable areas. Two miles from Gell's cottage stands the Sovereign Harbour complex, a development of luxury homes that will eventually total 3,000. Critics point to a major flaw - the development lies largely below the high-tide mark, doubling the number of people living in the Pevensey Bay flood risk zone.
The Environment Agency has expressed concern over the site, whose designer homes lie below the shingle buffer made to protect it from the sea. A spokesman for the development said the harbour was designed to cope with tides so large they are seen only every 400 years. 'The trouble is that 400-year tide might come tomorrow,' he said.
The following correction was printed in The Observer's For the record column, Sunday October 13 2002
We reported on the risk of flooding caused by the gravitational effects of the alignment of the sun and moon, a phenomenon we mistakenly described as 'the autumn equinox'. The equinox is simply the time of year when night and day are equal. In the autumn, this occurs around the 23 September, more than two weeks earlier than the predicted flood problems.