Motorists in England and Wales will be given two months' grace after the introduction of a law on Monday banning mobile phone use.
Using a hand-held phone while driving will become an offence
However, police in Scotland said there would be no such concession.
Using a mobile phone without a hands-free kit will be an offence incurring a £30 on-the-spot fine from 1 December.
The Association of Chief Police Officers (Acpo) issued guidelines which mean motorists in England and Wales will initially escape fines.
But motorists north of the border will be liable for fines from Monday because Acpo Scotland has not issued the same guidelines.
WHAT ARE THE NEW RULES?
Apply from 1 December
New offence of "using a hand-held phone while driving"
£30 fixed penalty fine
Rising to up to £1,000 if the matter goes to court
Rising to up to £2,500 for drivers of vans, buses, coaches and lorries
Officers in England and Wales have been told to give verbal warnings until February in order to "assist in the education of drivers".
Officers will still be able to hand out instant fines to mobile phone-using motorists if serious potential danger is caused or if their use contributes to a collision.
A spokeswoman for Strathclyde Police said she did not know why different rules were being applied in different parts of the UK.
She said: "The law will be enforced on Monday.
"Obviously officers will be able to use their discretion but we are not saying anything about a two month settling-in period."
Chief Inspector Bob Barbour from Strathclyde police said: "The use of a hand-held phone while driving is extremely dangerous and irresponsible.
"Driving requires a high level of concentration and it's vital motorists keep their hands on the wheel and not on their phone."
Loss of concentration
Scottish Transport Minister Nicol Stephen welcomed the ban.
He said: "Using a mobile phone whilst driving is dangerous.
"Phone calls and text messages can cause distraction for drivers and can result in loss of concentration which puts drivers and other road users at risk.
"These new measures will make our roads safer for us all."
Under the new law, £30 fines could rise to £1,000 if the case goes to court while drivers of heavy goods vehicles, buses and coaches may forced to pay as much as £2,500.