Christian Solidarity Worldwide has urged the Prime Minister to address freedom of religion or belief in China during his official three-day visit to the Asian superpower this week.

Chief Executive of CSW, Mervyn Thomas, has written a letter to David Cameron in which he expresses the organisation's concerns about reports of growing restrictions on the freedom to practise religion in China.

Although the right to freedom of religious belief is guaranteed under Article 36 of the Chinese Constitution, that protection is limited to those who worship within state-sanctioned religious bodies. Those who choose to practise their faith outside of these, or whose beliefs are not officially recognised by the Government, face accusations of participating in illegal activities, which carries a heavy punishment.

In the letter, Mr Thomas reminds Mr Cameron of those who are suffering persecution as a result of their faith, with particular attention given to the treatment of Protestant Christian house church leaders.

House churches, otherwise known as 'underground churches', which are unregistered and operate independently from the state Church, are regularly raided. In addition, they can be accused of illegal assembly and ordered to close.

One such raid took place in April of this year, after which Christians in Xinjiang province were interrogated on suspicion of belonging to a cult. Armed police forced their way into the leader's home, ransacked the property and arrested members.

One of China's best known Christian leaders, Pastor Samuel Lamb, was regularly arrested and spent 20 years in labour camps as a result of his refusal to merge his house church with that of the State. He died earlier this year.

More recently, on November 15, Pastor Zhang Shaojie was arrested along with 23 of his church members in Henan Province. This raid was unusual as the church in question was government approved, but members suspect that the arrest was linked to outreach programmes run in the local city. Human rights lawyers have thus far been obstructed from visiting those who have been detained.

Other concerns highlighted in CSW's letter are restrictions being placed on Uyghur Muslims in the Xinjiang Uyghur Autonomous Region, the plight of long-term Catholic prisoners, and the harassment, imprisonment and even torture of lawyers and activists who defend the right to worship freely.

"We believe that freedom of religion or belief is a touchstone for human rights standards in a nation," says Mr Thomas.

"On the occasion of this visit to China, CSW calls on the Prime Minister to encourage the Chinese authorities to treat all religious believers with equal respect in line with their commitments under domestic and international law."

Mr Cameron arrived in Beijing on Monday, and is meeting with businessmen and students to discuss growth and reform in Shanghai today.