Knife crime is rising at a much steeper rate in the home counties and rural provinces than in London, police figures show, amid signs that the growing use of blades is spreading from the cities to the shires.

Guardian analysis of official statistics shows a 45.7% average increase in knife-related offences in 34 English and Welsh counties since 2010, compared with an 11% rise in the capital.

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In the home counties, knife crime has risen by an average of 44.8% over the past eight years. Kent recorded the biggest increase of such crimes in England and Wales, up 152% since April 2010.

Police chiefs and experts said the figures were partly fuelled by gangs targeting new customers in rural areas, known as the “county lines phenomenon”, which they said was causing an “overspill” of criminality from the cities to the provinces.

Dr Rick Muir, the director of the independent policing thinktank Police Foundation, said: “Previously, the people selling drugs in Margate or Blackpool would be from those areas. Whereas organised criminal gangs in the bigger cities are exporting drugs directly into these areas.”

The murders of two 17-year-olds, Jodie Chesney in London and Yousef Makki in Greater Manchester, has prompted police chiefs to demand at least £15m in urgent funding to tackle what one of England’s most senior officers described as a national emergency.

Ten teenagers have been stabbed to death in London, Birmingham and Greater Manchester since the start of the year; Sunderland also had one such death. The number of knife crime offences remains far higher in the major cities, but the increase since 2010 is steeper in the provinces.

Knife crime is up 11% in London between April 2010 and September 2018. But in the home counties the increases are far higher, albeit from a smaller base. Knife crime incidents in Hertfordshire are up 89%, from 272 offences to 513; Essex is up 43%, from 536 to 766; the Thames Valley is up 43%, from 996 to 1,431.

Figures for Kent show a threefold increase in knife crime, from 346 incidents to 873, over the eight years. Assistant chief constable Nick Downing, of Kent police, said the rise was partly explained by improved recording methods and starting from a smaller figure, however he said the force would not “hide away” from the fact there had been an increase in knife crime.

In the West Midlands, knife crime in the Birmingham police area is up only 3% since 2010, but there was a 42% average increase in the neighbouring provinces of Staffordshire, Warwickshire and West Mercia over the same period, from 959 offences to 1,363.

In Staffordshire, the region between Manchester and Birmingham, knife crime has risen 88%, from 367 offences in 2010 to 689 last year. Supt Ricky Fields, Staffordshire police’s lead officer on knife crime, said county lines drugs gangs were partly fuelling the rise.

“The correlation we think it is attributed to is around county lines, urban street gangs,” he said.

“Staffordshire sits on an arterial route between Manchester and Birmingham and some of our neighbourhood areas have seen an overspill around the travelling criminality and bringing crime into that particular community [from the cities].”

Muir said county lines gangs were often using children to export drugs into provincial towns and that evidence showed a correlation “between knife crime – the offenders and victims – and the drugs trade”.

He added: “They operate on the basis of profit and the county lines model is more lucrative for them. Violence is then used to either deter or suppress the competition or it is being used by the criminals to discipline people in their own network, particularly children.”

Muir claimed there could also be a possible link to the increase in schools exclusions and the cuts to youth services.

“Lots of different things can happen and each on their own might not lead to anything significant but if they all happen in tandem you can get quite a big shift as is the case here,” said Muir.

Craig Kelly, a criminology lecturer at Birmingham City University, said the data showed that knife crime is a national issue and that politicians, media and academics were “far too focused on London”.

He said: “We’ve focused predominantly on knife crime and violence in London for generations. We’ve literally forgotten to ask what happens to the young lad growing up in Wythenshawe or Longsight [in Manchester].”

Kelly said Britain was in the grip of a cyclical spike in knife crime, after a surge of violent offences in 2008 and in the early 1990s. “It always comes after we’ve had some kind of economic turmoil,” he said.

Meanwhile, John Apter, the head of the Police Federation, called on the government to set up a multi-agency group to tackle the “national crisis” exacerbated by the “decimation of youth services” and the increased drug dealing across county lines.

He said: “Understandably the focus has always been on larger cities such as London and Manchester but the problem of knife crime is indiscriminate and it is increasing in other areas at an alarming rate.

“Whether it is gang culture or certainly the cross-county drug dealing – it means people will travel out into the shire forces, the smaller forces, more rural forces to commit their criminality and they will have knives with them or other weapons and they are not afraid to use them.”

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Apter, who has been a police officer for 26 years, said the government risked failing a whole generation of young people if it did not change its approach.

“The prime minster needs to do a lot of reflecting because she has got this wrong on a monumental scale. This is a massive, considerable problem and the police need a lifeline which can only be provided through genuine tangible investment,” he added.

A Home Office spokesperson said: “The home secretary has made clear that the rise in serious violence across the country is deeply concerning.

“The Home Office is working hard with police and other partners to tackle violent crime on many fronts and across the whole country.”

The spokesperson added that Sajid Javid had recently met “senior police officers and partners to discuss what more can be done.”

Additional reporting by Niamh McIntyre

• This article was amended on 14 March 2019. An earlier version said nine teenagers had been stabbed to death in London, Birmingham and Manchester. The last location has been corrected to Greater Manchester and the figure for those three places, to 10.