Hundreds of people have been evacuated from their homes and thousands are without power after widespread flooding in the North West, with more rain forecast.
Lancashire and Yorkshire have been hit by downpours, with people in a number of towns and villages forced to leave their homes after being stranded by rising waters.
As of 4.20pm on Saturday the Environment Agency (EA) had issued 20 severe flood warnings - which signal "danger to life", while there were 225 flood warnings, meaning that immediate action is required.
The Met Office also issued two of its most serious red weather warnings - danger to life - for the area.
Residents in Whalley and Ribchester in Lancashire were forced to abandon their homes when flood waters poured through the streets after torrential downpours.
Lancashire Fire and Rescue Service warned people to stay away from affected areas and told motorists not to drive unless they have to.
Flood sirens sounded at Walsden, Todmorden, Hebden Bridge and Mytholmroyd in Calderdale, Yorkshire, as the water breached defences.
About 10,000 homes in Rochdale and Lancashire lost their electricity supply after a main substation was damaged.
Electricity North West said extra engineers have been on standby and teams are working to restore power.
Mark Williamson, operations director for Electricity North West, said they were working in "extremely difficult conditions".
"We have drafted in extra engineers and will continue to work throughout the day to get everyone back on and we are here 24 hours a day, seven days a week so please contact us if you need any advice or information," he added.
Fire crews were forced to evacuate after a station in Padiham, Lancashire, flooded.
A 200-year-old former pub was destroyed by flooding at Summerseat, Greater Manchester.
Part of the ancient building, which sits on a bridge over the River Irwell, was swept away in the raging waters.
Alison Baptiste, EA flood duty manager, said: "Our thoughts are with all those who've been coping with serious flooding to their homes and businesses repeatedly over Christmas and those who face the risk of further flooding.
"On Boxing Day we have issued several severe flood warnings meaning a risk to life, we urge people to check their flood risk, prepare for flooding, follow advice from emergency services and never to risk driving through flood water."
A number of Boxing Day football and racing events were called off, including the Welsh National in Chepstow and Blackburn Rovers fixture.
Troops from the 2nd Battalion, Duke of Lancaster's Regiment, helped communities across the North West build miles of temporary flood defences and evacuate residents to safety.
The Met Office issued a yellow warning of rain for parts of north Wales, northern England and southern Scotland. The Scottish Environment Protection Agency issued eight flood alerts and 14 flood warnings.
Peter Box, environment spokesman for the Local Government Association, said councils are "pulling out all the stops" to find accommodation for people made homeless by the flooding.
"Plans have also been put in place to ensure that older and more vulnerable people are not put at risk and can still access the council help they rely upon," he added.
The Government's emergency Cobra committee held a meeting on Christmas Day and on Saturday morning in response to the flooding.
Environment Secretary Elizabeth Truss said: "I would like to again to pay tribute to the tireless work of front line staff over the last month and the Christmas period, and the extraordinary resilience of the people affected, which I have seen first hand.
"My thoughts and sympathy continue to be with people flooded out of their homes this Christmas and I can assure them we are doing everything we can to help communities recover from these storms."
Lancashire Fire and Rescue Service said it had been called out to around 350 incidents and rescued 50 people during the floods on Boxing Day.
All its boats and fire engines were mobilised to cope with the rising tide of incidents, the force added.