Flood warnings are in place across England and Wales and events have been cancelled due to heavy rain.
In Yorkshire, where the Cycling Road World Championships is taking place, organisers changed the route due to concerns for safety.
The Regatta London race on the River Thames was cancelled and forecasters have warned of more rain on Monday.
The wet weather also led to travel disruption, with road closures and delays to rail services.
A spokesman for the cycling race said the decision to re-route riders followed advice from the Environment Agency and local mountain rescue teams.
"We know this will be hugely disappointing to the communities in these locations who have been planning events and celebrations to coincide with the race. We are very sorry."
The Elite Men's Road Race, which started in Leeds, finished in Harrogate at an earlier time due to the route being shortened.
A fan zone set up in the spa town to allow spectators to watch the race on a big screen was closed after the site became waterlogged.
Train operator Northern Rail said services had been cancelled or disrupted across the North West.
Trains between Blackpool and Preston have been suspended due to floodwater on the line in the Poulton le Fylde area.
Trains are running at reduced speed on the West Coast mainline north of Preston and between Leeds and Harrogate, Manchester and Sheffield and Manchester and Newton Le Willows.
The village of Tarleton, near Southport, saw roads closed due to flooding and water levels rising in the nearby River Douglas.
John Stanley, who owns a business in the village, said: "It's quite bad; the roads and town centre are flooded. The shops are closed."
In parts of Wales, roads have been closed, trains have been diverted to different lines and some areas have had power cuts.
South Wales Police advised motorists to leave extra time for journeys as "driving conditions remain very poor", with some cars becoming trapped in flood water.
Bridges were being inspected in Aberdeenshire after heavy rain in north-east Scotland on Saturday caused flooding.
In Sussex, a man died and two other people were seriously injured when a car hit a tree and overturned in heavy rain near Fontwell.
Two people and their dog had to be rescued after becoming bogged down during a camping trip in Dartmoor National Park .
The emergency services said they were called at about 02:00 BST but the pair were unable to say where they were in the "extremely poor" conditions.
Four hours later, the man and woman, in their late 20s, were found by Dartmoor Search and Rescue Team.
In Derbyshire, police said there had been two crashes in the space of an hour on the A50 in Doveridge, tweeting that motorists had been driving "too fast for the conditions".
Alex Burkill, from the Met Office, said: "We've already seen some fairly significant rainfall and there will be further persistent rain through northern and central England and further showery outbreaks in Wales."
He said conditions would be "pretty fine" for most places at the start of Monday but "a system was going to come in through the day reaching south-west England and Wales by 10:00 BST".
Another 70mm could fall over the highest areas, which would be falling on to already saturated ground, he said.
"By evening rush hour, much of England and Wales will be pretty wet... It's not going to feel pleasant by any means."