Knives are being carried in the West by more and more people, shocking new figures show.

The number of people convicted or cautioned for possessing a bladed or pointed article went up 271 per cent (almost four times) from 1997 to 2007.

The most up-to-date crime statistics were obtained by the Conservative Party and show worrying trends in the region's police force areas.

The figures were unveiled as it emerged yesterday that a political aide at No.10 overruled the objections of Government statisticians over publication of knife crime figures.

The unnamed special adviser was "adamant" the numbers should be released, despite objections from the chief statistician at the NHS, the Public Administration Select Committee heard.

Data which appeared to show a fall in the number of youngsters being treated in hospital for stab wounds was put out by the Home Office in December, in a blaze of publicity about the Government's crackdown on knife crime.

The release of the information was later condemned by head of watchdog the UK Statistics Authority, Sir Michael Scholar, as "premature, irregular and selective".

However, these new figures show that there were 200 people convicted at magistrates' courts in the West for illegally having a knife in 1997, compared to 573 a decade later.

And cautions for the offence rose from 40 to 318 over the same period.

Avon and Somerset police, who cover Bristol and Bath, saw the most significant rises, with total cautions and prosecutions jumping from 61 to 347 – more than fivefold.

The figures also show that while no one was cautioned by the force in 1997, and only three in 1998, 147 were cautioned two years ago.

Chris Skidmore, the prospective Conservative MP for Kingswood, Bristol, said: "These figures reveal that the real and worrying problem of knife possession is getting worse in our local area, with a massive increase since 1997.

"Yet more people are being let off without facing justice for their crimes.

"The Government should be sending out a message that they will crack down on knife crime, rather than letting more than 40 per cent of offenders off with a caution.

But Avon and Somerset police's Superintendent Nigel Rock strongly disagreed.

"The chance of becoming a victim of knife crime in the Avon and Somerset force area is very small," he said.

"We take knife crime extremely seriously and use a range of tactics to reduce it. Officers will stop and search anyone who they suspect to be carrying a knife and those who are found to be doing so will dealt with robustly.

"There is no need to carry knives or bladed weapons and I would warn people that the consequences of carrying knives can be fatal.

"In recent years we have also held a successful amnesty which saw more than 500 knives handed in, including both domestic knives and weapons."

Dorset, Gloucestershire, Wiltshire, Gwent and West Mercia police (who cover Herefordshire) all handed out significantly more cautions and pursued more prosecutions over the 10-year period after Labour came to power.

In Gloucestershire, convictions more than doubled to 48 in 2007. Cautions went from none in 1997, to 29 in 2007.