Flood warnings are in place across England and events have been cancelled due to heavy rain.
In Yorkshire, where the Cycling Road World Championships is taking place, organisers said the route had been changed due to concerns for safety.
The Regatta London race on the River Thames is cancelled while forecasters warned of more rain on Monday.
The wet weather has also led to travel disruption, with a mudslide covering a railway track on Saturday.
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 today. We are very sorry.”
The Elite Men’s Road Race, which started in Leeds, is due to finish in Harrogate at an earlier time due to the route being shortened.
A Northern rail spokesman said the fanzone in Harrogate was also closed for the day due to weather and advised spectators to check for updates.
Steve Hopkinson, regional director at Northern, said: “The change of route, and the closure of the fanzone, will be disappointing for cycling fans – but we still expect thousands of people to travel to Harrogate to see the conclusion of the race.”
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 is 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 added.
“By evening rush hour, much of England and Wales will be pretty wet… It’s not going to feel pleasant by any means.”