Large numbers of the rodents are being displaced from their nests, and seeking shelter in nearby buildings, pest controllers said.
John Davison, Chief Executive of the National Pest Technicians Association, said that while there may not be more of the creatures around, they were becoming more visible as they moved away from flooded areas.
He said that the creatures tended to move in large numbers late at night, descending on the nearest place where they could find food - most commonly farms or populated areas.
He said: "Rats don't like to be in wet conditions any more than we do, so they will go to higher ground and enter domestic environments.
"Some built-up areas are experiencing heavier infestations, because they tend to go for anywhere where they can find bins or other forms of food.
"Because the rats move during darkness hours, they pick up others on the way and it becomes a movement of rats.
"You end up with quite a large number of rats if there are enough of them in the area, and you can get quite large movements.
"Normally they start to spread out again once they reach a town, but if it's an isolated home or a farm they will stay together in those numbers."
David Cross, head of technical training academy at Rentokil, warned that the rats were also more likely to spread diseases in flooded condition.
He said: “Rats carry a particular health risk in flooded areas, as their urine contains leptospires which can survive outside the rodent’s body for longer periods in wet conditions.
"These bacteria can cause leptospirosis or Weil’s disease in people. Anyone in contact with flood water where rats may have been active is advised to cover any cuts with waterproof plasters, wear waterproof gloves and to avoid swallowing any water.
"Simple things like ensuring that food waste is properly sealed and disposed of can make a big difference, as can sealing any obvious holes in the exterior of your property with wire wool or caulk.”
Cancer specialist Dr Anne Kiltie discovered first-hand how the floods were affecting the movements of rats, after one began eating her sofa bed and door frame.
The 49 year-old clinical oncologist, from Oxford, said that she was first alerted to the rodent's presence when she came home and found rice from a doorstop in her bathroom spilled in a trail across the floor.
She said she believed it climbed up through the toilet plumbing, as there were splashes of water on the floor and the toilet seat was damps.
She added: "To my horror chunks of wood had been gnawed from the door frame through to the kitchen the next morning.
"It was clear from the trails it had made that it had made a nest in the mattress of my sofa bed."
She put down rat poison and told neighbour Tim Lowe, who offered to deal with the rat before it caused more damage.
They set up a clear path for its escape to the garden and came face to face with the creature as they dismantled the piece of furniture it had made into its den.
Dr Kiltie said "As I was taking the bottom cushion away, I saw this nine-inch long brown rat.
"Even though it had been poisoned it was still scurrying about in the well of the sofa and it escaped behind the back of a nearby cupboard.
"It kept peeking out and at one point, when we moved the cupboard, it got up on its hind legs and looked at my neighbour.
"After that it made its exit and ran off into the garden.
"The room was a mess and the mattress of the sofa was chewed up so it's been thrown away."
Oxford is on the River Thames which has reached flood levels in the past two weeks.
A city council spokesman said the advice is to protect doorways and put bungs in ground-floor toilets during flooding.
Public Health England advised people dealing with rat problems not to approach live animals and to dispose of dead creatures hygienically.