The covert operation saw officers ‘spying’ on and filming unsuspecting motorists from the top of the National Express vehicle.

Forty-five drivers were caught in the first three hours – with one woman spotted eating cereal at the wheel.

Twitter users branded the operation, carried out on the Birmingham Road, near the Scott Arms pub in Great Barr, a waste of police resources.

While Jonathan Chambers said: “Haven’t got time to attend someone’s house after they’ve been burgled, but got all day to sit on the top deck of a spy bus to bust drivers who aren’t even moving.”

But Chief Constable Dave Thompson insisted it could save lives.

He said: “Seen the debate on the priority/use of resources on this – A: It is a cause of fatal accidents. B: Short-term, high-impact, low-resource ops create huge impact on motorist behaviour. C: Critical feature is getting public to self report. This will change behaviour at low cost.”

Thirteen drivers took part in a virtual-reality education course at the side of the road, allowing them to see crashes caused by drivers on phones.

The other 32 will be sent prosecution notices in the post and could be fined and receive points.

Wolverhampton councillor, Phil Bateman, who was previously divisional corporate affairs director at Travel West Midlands, said this type of operation was crucial to help change the way motorists think.

He said: “The law is the law. If people are breaking the law they do so with the full expectation they could get caught at some stage. How the police catch them is another issue.

“I don’t see a problem in trying to deal with a difficult law in the way they have explored doing.

“It is no different from people being under surveillance for other offences.

“It carries huge support from the general public in regards to the fact people shouldn’t be using their phones while driving. It can be tempting to use a mobile phone but it is breaking the law and they should be aware people around them can report it.