Junkies in Birmingham are becoming further entrenched in their habits as pushers offer a lethal crack and heroin 'buy-one-get-one-free' deal.

The charity DrugScope found that the combination of the substances - popular for its stimulant-sedative properties - was now being treated as a drug in its own right.

In a speedball, heroin and crack are injected together from a single syringe, and it leads to speedballers injecting more times in the same day.

The spiralling trend raised the prospect of even more burglaries, robberies and other thefts being committed by addicts to fund their costly habits, DrugScope claimed.

A recently conducted survey of 100 drug addicts, published yesterday by the charity found that speedballers had three times as many convictions as those only using heroin.

It said speedballers spent £500 a week on the drugs - a staggering £26,000 a year - compared to £110 for heroin-only junkies.

The survey also revealed that speedballing was the main method of drug-taking for 80 per cent of those interviewed, compared with 25 per cent a decade ago.

The trend could also increase overdoses and viral infections among addicts, DrugScope added. The charity compiles an annual league table of the price of drugs in 20 cities across the UK and surveys 80 treatment agencies and police forces.

Overall prices for drugs in Birmingham are slightly below the national average.

Birmingham was the second cheapest place to buy heroin and cocaine.

"The general picture is that overall the price of drugs in the last ten years has come down dramatically," said DrugScope magazine editor, Harry Shapiro.

"Speedballs hadn't come up on the radar until the last year. It is reflection on the way heroin and crack are being

marketed on the street - the two-for- one offers and the buy-one-get-one free offers. It is because there are so many dealers out there.

"Many of the users would be familiar with both drugs anyway, so the addition of one or the other would be attractive."

Drug users already taking substances such as methadone and alcohol often use tranquillizers as well and in Birmingham diazepam is also on offer at extremely low prices (5p per tab or £1 per strip), and is readily available.

Cocaine use among people who would not otherwise break the law was also still increasing at a steep rate, he said.

"Cocaine has come down in price a lot, but it still retains a champagne image because models and rock stars are still associated with it," said Mr Shapiro.

"From what we can tell there is a lot of it about in Birmingham and a lot of ordinary people, who are otherwise law-abiding, are snorting cocaine as part of a normal night out and not thinking they are breaking the law."

Some areas, including Gloucester and Penzance, reported "dramatic drops" in the price of heroin and crack due to dealers targeting the area, the charity reported.