Severe flood warnings have been issued for large areas of East Anglia as high tides and strong winds threaten to swamp the coastline.
The Environment Agency has issued 18 alerts for the region, warning of severe flooding and danger to life.
Residents in areas including West Mersea in Essex, Southwold and Thorpeness in Suffolk, the Riverside Business park in Lowestoft, Suffolk, and along the Bure and Yare rivers in Great Yarmouth are likely to be affected.
By 7am the EA had issued 140 flood alerts across England and Wales with 3,000 properties expected to suffer from flooding in the next 24 hours.
EA spokesman Peter Fox said: "The most important thing is that along the east coast (of England) the high tide will be hitting in the hours of darkness this evening and tonight, so people really need to take the daylight hours today to prepare for the coastal and tidal flooding that we are predicting."
Mr Fox said evacuation in "key areas" was being discussed with the police.
Gusts of more than 90mph have been recorded in Scotland, according to MeteoGroup, the weather division of the Press Association.
A gust of 92mph was recorded at Loch Glascarnoch in the Highlands, of 89mph at South Uist in the Outer Hebrides and of 72mph at Malin Head in Northern Ireland.
The gale-force winds threaten to whip up the most serious tidal surge for 30 years.
In some places, sea levels could be as high as those during the the devastating floods of 1953, the EA said, although flood defences since then, including the Thames, Deptford and Hull barriers, should provide better protection than 60 years ago.
There was also disruption this morning on a number of rail routes, including East Coast trains.
Areas most at risk of flooding include the North Sea coast from Northumberland down to the Thames Estuary and Kent.
The EA has issued a severe flood warning - the highest category, warning of danger to life - to homes and businesses near The Quay in Sandwich, Kent, for high tides between 12.45am and 1pm tomorrow.
The tidal reaches of the River Trent, Nottinghamshire, could also be affected today.
On the west coast, severe gales and large waves combined with high water levels are also expected from Cumbria down to Cheshire.
The Thames Barrier was closed last night to protect London, and other defences have been activated at Colne in Essex and in Hull.
Natural Resources Wales is urging people along the north Wales coast between eastern Anglesey and Liverpool to be prepared for flooding today.
Dr Paul Leinster, chief executive of the EA, said: "Gale force winds and large waves along the east coast of England are forecast during Thursday and Friday, coinciding with high tides and a significant coastal surge.
"Flooding of some coastal communities is expected and some defences could be overtopped by the combined effect of high tides, high winds and a tidal surge.
"Coastal paths and promenades will be highly dangerous as there is an increased risk of people being swept out to sea.
"The Environment Agency is monitoring the situation closely, working alongside partners including the emergency services, Met Office and local authorities. Environment Agency teams are out on the ground checking that flood defences and barriers are in good working order, monitoring sea levels and issuing flood warnings."
The Met Office has issued a wide range of weather warnings, with winds expected to gust to more than 80mph as they swing north-westerly in mid-morning, with gusts of more than 90mph in exposed parts.
Much of Scotland faces "be prepared" warnings for wind and lesser "be alert" warnings for snow, while north west and north east England, Yorkshire and Humber, the Midlands, and the east of England are under "be prepared" warnings.
A major traffic route into Leeds city centre, past Bridgewater Place tower - the tallest building in Yorkshire - is being closed today after predictions that wind speeds in the area could reach 75mph.
Only South Wales the South West and southern parts of England will escape the high winds, which will ease during the afternoon.
The Environment Agency warned that high water is due between 10.30pm and 10.45pm, when tide levels will be more than 3 metres. Surges of almost 2 metres are expected.
The EA issued a severe flood warning - the highest category, warning of danger to life - to homes and businesses near The Quay in Sandwich, Kent, for high tides between 12.45am and 1pm tomorrow.
The areas with severe flood warnings in Anglia are:
:: West Mersea in Essex, The Strood and adjacent marshland;
:: Southwold in Suffolk and surrounding marshes;
:: the villages of Snape and Iken in Suffolk, and surrounding marshland;
:: Aldeburgh and Thorpeness in Suffolk;
:: Blythburgh in Suffolk and the marshes upstream of the A12;
:: Riverside Business Park in Lowestoft and Kirkley in Suffolk;
:: south bank of Lake Lothing and Bourne Business Park to Mutford Lock in Lowestoft;
:: Oulton Broad near Mutford Lock in Lowestoft;
:: the north bank of Lake Lothing;
:: the River Bure in Norfolk, from Scare Gap to the Euro Centre Industrial Estate at Great Yarmouth;
:: Lowestoft Seafront and Docks;
:: t he River Yare in Great Yarmouth at South Denes, from Wimpey Quay to the sea;
:: t he River Yare at Great Yarmouth from the pilot station to lower ferry;
:: t he Rivers Yare and Bure at Great Yarmouth from South Quay to Bure Park;
:: the River Yare from Gorleston-On-Sea in Norfolk to Breydon Bridge including Southtown and Cobholm Island;
:: the north Norfolk coast at Salthouse;
:: the north Norfolk coast at Blakeney;
:: the north Norfolk coast at Wells Quay
Thousands of train passengers in the north of England and Scotland were affected by reduced or cancelled services and the imposition of speed restrictions.
Train companies were operating amended timetables, with the changes likely to last until the afternoon.
Among many services affected was Leeds-Doncaster where operations were disrupted by debris on overhead wires near Leeds.
No ScotRail services were able to run before 7am and many other routes were not operating at all. Some services in Scotland were not expected to start until 4pm.
On First TransPennine Express, no trains were able to run between Newcastle and York apart from the 6.11am, while only the 5.36am and 7.42am ran between Carlisle and Edinburgh/Scotland.
Virgin Trains planned to run a normal timetable today with the exception of trains between Preston and Edinburgh/Glasgow Central which could be delayed by up to two hours or cancelled.
On CrossCountry services, no trains were able to run between Edinburgh and Glasgow Central/Aberdeen, while j ourney times between Edinburgh and York were being extended by up to two hours. Trains that normally start/terminate at Newcastle were starting/terminating at York.
To add to travellers' difficulties, there were delays through Birmingham New Street due to signalling problems.
Further south, poor rail conditions at Tunbridge Wells in Kent led to delays to services between Hastings and Tonbridge, while a signalling problem at Gatwick led to delays to trains serving the West Sussex airport.