Storm Ciara has brought winds of 97mph, cancelling flights, rail services and sporting events including a Premier League game.
A "major incident" has been declared by Lancashire Fire, with the Energy Networks Association reporting that 539,000 households have so far been hit by power cuts.
Video posted on Twitter by Big Jet TV showed a British Airways plane aborting a landing at Heathrow as it battled against the high winds.
There are more than 200 flood warnings, meaning flooding is expected and immediate action is required, and more than 150 alerts indicating flooding is possible.
Motorists are being warned to take extra care on the roads due to the potential of difficult conditions caused by strong winds and heavy rain, as emergency services reported lucky escapes from flooding and fallen trees in regions.
A man was trapped for more than an hour before he was freed by firefighters after his car was crushed by a fallen tree in Flitwick, Bedfordshire.
"Remarkably" he suffered "very minor injuries," tweeted Beds, Cambs & Herts Roads Policing Unit, adding: "Luckily the child seat was empty at the time."
Firefighters in Blackpool rescued a driver whose car became stuck in floodwater.
"It's been a busy night responding to flooding incidents along with a flood rescue this morning," South Shore Fire Station tweeted.
North Yorkshire Police said it had received reports of flooded roads, fallen trees, a shed blowing into a street and an escaped cow, with a force spokesman saying: "No corner of the county has escaped today's bad weather".
The town of Appleby-in-Westmorland in Cumbria was hit by severe flooding as the River Eden burst its banks, with residents battling to protect their homes.
Cumbria Fire and Rescue Service urged people not to drive through floodwater after they rescued a number of motorists.
One side of a wall belonging to Sonia's Bistro, on the banks of the River Teviot in the town of Hawick in the Scottish Borders, collapsed and was washed away.
The Met Office has issued weather warnings with the storm set to be the most intense in Britain since 2013.
Winds have already reached 97mph in The Needles in the Isle of Wight and 93mph in the fishing village of Aberdaron in Wales, while Cumbria has seen 151.8mm (6ins) of rain in 24 hours, it said.
It has also issued an amber warning for much of England and Wales until 9pm, saying "widespread gales" could cause damage to homes and businesses, travel disruption and power cuts, and pose a "danger to life".
An amber warning for heavy rain covers parts of Scotland, while yellow warnings are in place across the entire UK.
Gatwick Airport said "very high wnds" were "causing some flight delays and cancellations".
Heathrow Airport said it had taken a joint decision with its airline partners to "consolidate" Sunday's flight schedule to minimise the number of cancelled flights.
A spokesperson added: "We regret any disruption caused and remain focused on getting passengers away safely and as quickly as possible."
Virgin Atlantic said it has axed a number of flights, while British Airways is offering customers flexible rebooking options on domestic and European flights flying to and from Heathrow, Gatwick and London City airport on Sunday.
BA said in a statement: "Like all airlines operating into and out of the UK... we are expecting to be impacted by the adverse weather conditions across parts of the UK."
Brussels Airport also saw delays or cancellations - and two huge ports on either side of the English Channel, Dover in England and Calais in France, shut down operations amid high waves.
The Queen broke her Sunday routine and did not attend church in Sandringham due to high winds in the area, Buckingham Palace said.
Authorities have urged people to stay away from a number of beauty spots and all eight Royal Parks in London have been closed as a precautionary measure.
They include Bushy Park, Green Park, Greenwich Park, Hyde Park, Kensington Gardens, Regent's Park and Primrose Hill, Richmond Park and St James's Park.
In a statement, The Royal Parks said: "The Royal Parks are home to over 170,000 trees spread across 5,000 acres, with a significant population of ancient and veteran trees that are vulnerable to high winds.
"We will be monitoring the forecast closely over the next 24 hours and if there are any changes we will communicate these via this website and twitter account @theroyalparks.
"All parks will reopen on Monday, as soon as it is deemed safe to do so."
Sky News weather presenter Kirsty McCabe said: "It's going to be a very windy day with damaging gusts likely to cause travel disruption in what is set to be our stormiest day since the St Jude's Storm of October 2013.
"As well as wind gusts of 60 to 80mph, heavy rain over western and northern hills may also lead to some flooding. And given the high spring tides there's also a risk of large waves and coastal flooding.
"Snow is likely over the Scottish hills with gales causing blizzard conditions."
Several rail firms are operating reduced timetables, with strong winds having the potential to damage overhead electric wires and tracks due to debris or trees falling onto the railway.
Leeds City station reported severe disruption to services and tweeted an image of the tracks between the city and Harrogate at Bramthorpe which showed a waterfall of rainwater gushing onto the tracks.
A trampoline blown onto train tracks by strong winds in Chelsfield, southeast London, disrupted rail services between Sevenoaks and Orpington.
Network Rail and train operators in England issued an alert to passengers, stating: "Only travel by train this Sunday if absolutely necessary."
Disruption could continue into Monday morning as repair work may be hampered by the conditions and passengers are urged to check for updates before travelling.
Firms that have issued "do not travel" warnings include Gatwick Express, Grand Central, Great Northern, Hull Trains, LNER, Northern, Southeastern, Southern, Thameslink and TransPennine Express.
The other affected lines are: Avanti West Coast, c2c, Chiltern Railways, CrossCountry, East Midlands Railway, Great Western Railway, Greater Anglia, Heathrow Express, Hull Trains, Island Line, London Northwestern Railway, London Overground, Merseyrail, Northern, ScotRail, South Western Railway, Stansted Express, TfL Rail, Transport for Wales and West Midlands Railway.
Ciara has already made its presence felt in parts of the country, as strong winds brought down the roof of a pub and injured three people in Perth in Scotland on Saturday evening.
Police put a cordon in place around The Venue so that the damage could be assessed and nobody is said to have been seriously hurt.
Staff at the pub posted on Facebook: "Unluckily tonight our neighbouring building's chimney breast fell through our roof causing the roof to cave in and the top front of our building to be dislodged."
Several bridges in Scotland were closed to lorries and other high sided vehicles on Saturday with the Erskine, Dornoch Firth, Skye and Kessock bridges among those affected.
There was also a 40mph limit put in place on the Queensferry Crossing.
Ferry passengers also faced disruption with many Caledonian MacBrayne services cancelled due to the weather.
The weather is also having an impact on sports events including horse racing, ruby union, rugby league ad football fixrures across the country.
Manchester City said it had postponed its Premier League fixture with West Ham due to "extreme and escalating weather conditions".
The Women's Six Nations rugby match between Scotland and England in Glasgow on Sunday was also cancelled due to the "extreme weather".
Scottish Rugby tweeted the "safety of travelling fans, players and venue staff was the priority", and said "discussions are under way around rescheduling the game".
The London Winter Run 10k event, which was due to be attended by 25,000 runners, was cancelled after organisers said they were "not able to guarantee the safety of our runners, crew and volunteers".
Galway 2020 also said on Twitter that it was "extremely disappointed" to announce the cancellation of the finale of its opening ceremony on Saturday evening because of the warnings.
Guy Addington, regional water safety lead at the RNLI, said: "This rough weather could making visiting our coasts around the UK and Ireland treacherous and bring very dangerous sea conditions.
"If you see someone else in danger in the water, call 999 and ask for the Coastguard. If you have something that floats that they can hold on to, throw it to them. Don't go in the water yourself - too many people drown trying to save others."
On Monday and Tuesday, up to four inches of snow is expected in parts of Scotland and Northern Ireland, with blizzard conditions forecast.
Storm Ciara follows Storm Atiyah, which hit between 8-9 December, and Storm Brendan, which brought wind and rain to the country in mid-January.
In October 2013, the St Jude storm battered southern areas, uprooting trees, shutting down bridges and rail services and grounding flights. Several people were killed by falling trees in separate incidents.
Just weeks later, a powerful Atlantic storm killed two people and threatened the east coast of England with the worst flooding seen in 60 years.
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