Thieves stealing copper from water works in Rainham could be in for a nasty shock as smart dyes and man traps become the latest tools in the fight against the crime.

Thames Water, Britain’s biggest water company, is losing �1.2m a year as a result of crooks stealing metal from its operational sites in the south of the borough and along the Thames estuary.

Soaring commodity prices are fuelling the underground market for copper, lead and other non-ferrous metals.

But Thames Water is fighting back, using ‘SmartWater’ - coded water which invisibly tags metal and any thieves who steal it.

It is almost impossible to remove.

Once daubed with the liquid, which shows up under ultra-violet light, any metal can be traced back to its owner - and the thief or receiver can be linked with the crime scene.

The water company is also working with police and security services to install covert traps to spray criminals in the act.

Rainham is one of the worst-hit areas, where �35,000 of copper piping was taken in the past year, in the form of earthing cable, lead roofs and galvanised metal grating.

Other hotspots are Aylesbury, Marlow, East Hyde and Bishop Stortford,

Bob Collington, Thames Water’s director of asset management, said: “Metal theft at our sites costs our customers millions of pounds to put right. We are dealing with this by applying a forensic signature to all our equipment, so anything taken from one of our sites can be traced back. This makes it very difficult for criminals to sell on stolen items without detection.

“Any thieves who target our property face being sprayed with forensic liquid, meaning they will carry evidence of their crime on their skin and clothing wherever they go – it’s a huge risk, for very little gain.”

Regular scrap yard checks will also be carried out across the Thames Water region and an increasing number of scrap metal dealers are also equipping themselves with UV lights making it very difficult for criminals to sell metal on.

The cost of a tonne of copper is now in excess of �6,000.