With its wooden floors, leather sofas and customers peering at their Apple laptops as they sip their coffees, Mocca Cafe is the not the den of iniquity that might normally attract a police raid.

But Islamabad's police have suddenly found cause to turn their attention to the capital's poshest eateries in an effort to enforce a patchily applied, decades-old law forbidding people from eating or drinking in public during the fasting month of Ramadan.

Customers and proprietors were shocked on Saturday when, nearly halfway through the holy month, Mocca and at least two other popular eating spots in the well-heeled Kohsar market were visited by police officers cracking down on the illicit consumption of muffins and brownies, not to mention smoothies and skinny lattes.

Members of what pass for Islamabad's cafe society said they could not remember anything like it. The manager of Gloria Jeans, a nearby restaurant, said he had never even read the Ramadan law until the police arrived. He has now placed a sign in the restaurant saying it is only "open to the communities not observing the fast of Ramadan".

A message circulated on an expatriate email list by a customer who had been in the Gloria Jeans coffee shop at the time reported a "large commotion".

"There was a lot of hostility in the air because foreigners were being served while others (Pakistanis) were being told to leave," the email said, before going on to advise expats to give restaurants a wide berth until the end of Ramadan.

"Personally, I wouldn't take the chance after the anger I felt while in the coffee shop."

The raids, which police say were prompted by a complaint from a member of the public, followed last month's police assault of a journalist who had the temerity to consume a soft drink in his car at a secluded hilltop beauty spot overlooking Islamabad.

He said he was beaten with belts by the officers, who threatened to charge him under the Ramadan Ordinance, a law passed in 1981 by General Zia-ul-Haq, the then military ruler who did much to make Pakistani society more Islamic.

Prior to the law, which allows for transgressors to be jailed almost on the spot for up to three months, restaurants simply covered their windows to conceal diners from public view.

The heavy-handed policing of eating raises fears among some critics of a rising tide of Islamic conservatism within the state and society at large.

"This sort of behaviour is totally unwarranted, and a sign of the extremism that has infiltrated into the police," said Raza Rumi, a newspaper columnist.

"We have this double standard where the police take no action on the important things but when it comes to enforcing these Islamist positions they are more efficient than ever," he said.

The police involved in last week's raids say they were simply enforcing the law. One senior officer, who did not wish to be named, said he was actually trying to discourage extremists.

"Personally I have no problem with people eating, but if the restaurants and hotels in the less privileged parts of the city are not serving food then it gives us an image problem with militants and religious people. They say the common people abide by the law, why don't you take action against the posh areas?"

The sensitivities of Pakistani liberals are all the more acute in Kohsar market. The small collection of shops and restaurants located between a mosque and a children's play area was the place where Salman Taseer, the governor of Punjab province, was gunned down by one of his government bodyguards in January 2011.

He was walking past Mocca Cafe when his guard, furious at Taseer's public defence of a Christian woman sentenced to death under the country's much-criticised blasphemy laws for allegedly insulting Islam, shot him dead.