Rats the size of cats that are becoming resistant to traditional poisons are now a major concern to pest control professionals.
The 'super rats' as they're being dubbed will require the use of stronger toxins, but these will first need to be approved by the Health and Safety Executive (HSE).
There's been a 15% rise in call-outs for pest controllers in the past year alone.
Whelan Pest Prevention boss Sean Whelan was quoted by the Liverpool Echo: “All around Merseyside there’s been a problem.
“We’re seeing bigger rats in Liverpool. They’re super rats in my opinion.
“Access to food is so easy for them. They’re like humans, they eat and eat and get bigger and bigger.
“They’re becoming very resistant to bait in Liverpool. Soon we’ll have to be putting third generation bait down which we will need to get legislation for.”
The poison used to kill rats in the 1960s and 1970s was based on warfarin (the blood thinning drug). The last major change was as recent as 2012 with the approved use of bromadiolone but experts now believe that this is already obsolete.