Churches are fighting back against metal thieves with a hi-tech liquid that can capture the criminals' DNA.

At least four churches in the county have been stripped of metal from their roofs by criminal gangs this year. The metal, principally lead and copper, is sold to scrapyards for a high price because of the demand from growing economies like China.

Now every Anglican church in Oxfordshire is to coat its roofs with a liquid containing a unique DNA-style forensic code which permanently marks the thief. The liquid can only be seen under UV light and cannot be washed off. Lead was stripped from the roof of St Andrew's Church in Chinnor earlier this year, causing water to pour into the building when it rained.

Rev John Kinchin-Smith said: "It is a sad reflection of these days that nothing is sacred any more. The last thing we want to do is make churches like fortresses, because they are part of the community and need to be accessible. But I am glad something is being done."

There have been about 40 insurance claims made by churches robbed of metals in the Oxford Diocese, which includes Oxfordshire, Buckinghamshire and Berkshire, this year.

The estimated insurance claims total about £150,000. Two years ago, only one claim was issued by a church in the diocese.

All Saints in Didcot and St Francis in Cowley, Oxford, have been targeted this year. In September, gangs stole copper and lead from the roof of St Mary's Church in Garsington - just days before it was due a £300,000 restoration, paid for by donations from the community.

The Rt Rev John Pritchard, Bishop of Oxford, said: "This is bad news for metal thieves and good news for everyone else. Church buildings are at the heart of our communities, visited by the whole community for a whole range of reasons during a year.

"That may be for a church service, wedding or funeral, a community meeting or maybe just for a bit of peace and quiet."

But non-toxic liquid, called SmartWater, will mean every church will have its own code so that the lead and metal can be traced back to the owner and criminals coming into contact with it can be linked to the crime scene.

SmartWater is also used by police across the country.