LAHORE: A 72-year-old British doctor is in prison in Pakistan for “posing as a Muslim”, charges that reveal an escalating ideological fight that often spills over into violence.

Masood Ahmad is a quiet, reserved widower who returned to Pakistan to open a pharmacy in 1982 after decades of working in London to pay his children's school fees, his family said.

He is also an Ahmadi. A 1984 Pakistani law declared them non-Muslims, and Ahmadis can be jailed for three years for posing as a Muslim or outraging Muslims' feelings.

Some clerics promise that killing Ahmadis earns a place in heaven. Leaflets list their home addresses.

Three years ago, 86 Ahmadis were killed in two simultaneous attacks on Friday prayers in Lahore.

There have been no mass attacks since then, but targeted killings are rising: last year 20 Ahmadis were killed, up from 11 in 2009.

And legal prosecutions are on the rise, say Ahmadis, some of which they say are linked to property grabs.

Ahmad was arrested in Pakistan's eastern city of Lahore last month when two men posing as patients questioned him about his faith and used mobile phones to secretly record him reading a verse from the Holy Quran.

“He (the patient) said you are like a father to me, please help me with some questions,” said the doctor's older brother, Nasir Ahmad. “When (my brother) answered, they began beating him and dragged him outside by his neck.”

One of his accusers, religious teacher Muhammad Ihsan, told Reuters that Ahmad had preached to them illegally.

Last year 20 cases against Ahmadis were registered, up from 10 cases in 2009.

A bank clerk was arrested for wearing a ring with a Quranic verse and an entire family was charged for writing a Muslim greeting on a wedding invitation.

Clerics have twice sought the arrest of an entire town of Ahmadis, 60,000 people, for holding religious celebrations.Residents were serving food, giving out sweets and displaying bunting, the complaints said.

“We would not have a problem with them if they did not use the name of Islam and the symbols of Islam,” said Tahir Ashrafi, head of the powerful Ulema Council of clerics.

“We are against the killing of any innocent... Such attacks are not acceptable or allowed, but if they break the law, we have a right to go to the police,” he said.

“His children watched him die”

There are about half a million Ahmadis in Pakistan, their leaders say. Many only feel safe in Rabwa, a town they bought when Pakistan was created in 1947. On its main streets, banks of security cameras monitor fruit vendors and dozing dogs.

Near the playing fields, blocks of flats house families that fled other parts of Pakistan after loved ones were murdered.

Rafiatta, who asked her last name not be used, moved to Rabwa after gunmen killed her husband in 2010 in front of their young children.

“He was just a hard-working man who loved his family,” she said. The family fled after two Ahmadi neighbours were also killed and men tried to kidnap Raffiata's young son.

The Ahmadi are also targets outside Pakistan.

In Indonesia,a gruesome YouTube video recorded a mass lynching in 2011 as police looked on.

Ahmadi publications are banned in Bangladesh, where a festival site was torched earlier this year.

In Britain, Ahmadi buildings have been vandalised and leaflets have appeared forbidding them to enter shops and urging Muslims to kill them, British media have reported.

But Pakistan is the epicentre of persecution.