Pakistan’s largest city, Karachi, is the bustling financial hub of this huge, turbulent nation, and perhaps not surprisingly it is one of the most dysfunctional cities in the world. As the US military chief General David Petraeus pointed out recently, the city has less electricity per capita than Baghdad. And if the lights go out, riots often erupt.

With the outside world increasingly worried about nuclear-powered Pakistan’s political meltdown and encroaching militants, there are also fears that the Taliban may soon gain a foothold in this sprawling former capital. Waseem Ahmed is the local police chief charged with keeping the city safe. Perhaps it’s because he faces such a daunting task that his tone of voice suggests he’s resigned to making only a tiny dent in the roll-call of crime and unrest. “Karachi is a mega city with complex, ethnic, sectarian and political divisions. People here have a large number of weapons,” says Ahmed.

Ahmed starts his day with melon for breakfast, sitting on a gold-sprayed chair at his home in the district of Defense before heading for his parquet-floored office in the city’s financial centre. He scrolls through the night’s texts on his mobile. The first – a TV station asking for extra security after receiving a terrorist threat. The last – three four-wheel drives “snatched” at gunpoint and 20 similar vehicles stolen.

Ahmed has been in the job for 18 months. That’s about as long as most last in the position. Since Pakistan was created 61 years ago, no civilian government has ever finished its term in office and police chiefs are replaced every time there’s a new government.

Karachi is a rapidly expanding mass of roughly 20 million people living around this port on the Arabian Sea. Traffic ­accidents here can quickly lead to ethnic ­violence and monsoon rains flood the poorly drained streets. Ahmed has a 30,000-strong police force for everything from tackling kidnappings to providing ego-boosting police escorts for politicians and rounding up drug-fuelled ravers on the beach. But most ordinary people have no confidence in the police.

“What is the perception of the police?” a visiting former supreme court judge Nasir Aslam Zahid asks a meeting of the city’s more senior officers. “Speaking frankly, it is above all that they are corrupt, inefficient and apathetic.” Officers are hesitant to make spot checks for weapons or drugs, Zahid says. “If we do arrest people we come under political pressure to release them,” says one officer.

And perhaps the greatest flaw in the system: police are reluctant to register cases as their performance is deemed to be better when they register fewer crimes. Ahmed has announced that performance will be judged on the number of crimes “detected”. Until ­recently, victims had to pay to report a crime.

When you see the equipment the Karachi police have, you begin to see why some feel it’s not worth trying to take on the criminals. With wooden boxes full of obsolete bolt-action Second World War Enfield .303 rifles, only a few modern weapons, and 500 sets of riot gear donated by the US, it seems woefully ill-prepared to take on the Taliban if they arrive in force.

“What we need the most are Armoured Personnel Carriers [APCs]: I have 23 but 12 are out of service,” says Ahmed, pointing to some broken, rusting APCs. “There is no money to mend them.” Meanwhile the police living quarters have no running water or sewerage. Between 7 and 10 per cent of the force has hepatitis.“We are short of manpower. On a citizen to police-officer ratio we are behind Delhi, Bombay and Lahore. You’re supposed to have one officer for 300, I have one for 600. I want to double the police force,” says Ahmed.

His phone buzzes again. This time to tell him an appeal has been dismissed in a case against “police high-handedness”. Then there’s the “land-grabbing” (political parties regularly steal chunks of land for development). And oil smuggling.

Analysts expect Karachi to face more violence as the Taliban and al-Qaeda ­respond to military operations in the north-west and US missiles targeting the border tribal areas. About 300,000 ethnic Pathans, from whom the Taliban have drawn their majority of recruits, have moved from the troubled areas and settled on Karachi’s outskirts.

People worry that if the Taliban surfaces in Karachi it will lead to clashes ­between Pathans and the dominant political force here, the Muttahida Qaumi Movement, whose leadership and supporters are Urdu-speaking Mohajirs whose families migrated from India at Partition. “It’s a very delicate situation,” agrees Ahmed.

Terrorism has struck this city in the past. In 2007, a suicide attack on the homecoming parade of former prime minister Benazir Bhutto killed 149 people. She was assassinated two months later in Rawalpindi. Individual police ­officers such as Superintendent Farooq Awam, who cut his teeth tackling Shia-Sunni sectarian violence, have emerged as key terrorism investigators.

A plain-clothes police officer enters to announce the arrest of a handful of militants, possibly Taliban. Ahmed has a file on his desk marked “missing people” – mainly Baloch nationalists or those suspected of Islamic militancy who are “disappeared” by intelligence agencies.

Eventually, he heads home where the power in the land is his wife, a civil servant previously posted to Washington. One of their daughters is a tennis player now called to the bar at Lincoln’s Inn in London. The other is studying at the London School of Economics. They are part of the brain-drain from Pakistan – ironically, something that a powerful police chief could help reverse by making the country safer.