New on-the-spot "litmus tests" are being introduced in a further clampdown on underage drinking.

The system is being tested in west Oxfordshire and has already claimed its first success.

All 20 police community support officers for the district are being issued with test packs to take out on the streets. The packs contain small chemically-treated sticks which change colour if dipped into alcohol.

Witney's neighbourhood policing manager, Sgt Scott Evans, said: "We often come across teenagers with big coke bottles or other soft drinks, saying that's all there is in it.

"Using these sticks we can carry out a simple test to see whether they are telling the truth."

The first test was carried out last week on a bottle carried by a teenager in Witney. It proved positive and the drink was poured away by a PCSO.

The test kits are being funded by the West Oxfordshire Community Safety Partnership and have been distributed to PCSOs throughout the district.

Since last October, when police seized a vast amount of alcohol from teenagers on Witney's Deer Park estate, the amount found on the streets has been decreasing.

Thames Valley Police spokesman Toby Shergold said: "There seems to be a corresponding decline in the incidents of criminal damage, so we think it is working.

The parents of under 18s caught with alcohol are notified and invited, along with their children, to attend Alcohol Awareness workshops.