In May 2018 the BBC Shared Data Unit reported one smuggled mobile phone or SIM card had been seized for every six inmates in English and Welsh jails in 2017.
We compared figures for the period 2010-2014 and 2017 from ministers' answers to written questions in Parliament, Freedom of Information requests to prison services in Scotland and Northern Ireland and published prison population figures.
Our analysis revealed the number of seizures in England and Wales increased from 9,600 in 2014 to at least 15,000 last year, a 56% rise.
The rate of finds across prisons in England and Wales doubled from an average of nine discoveries for every 100 prisoners in 2011, to at least 18 per 100 prisoners in 2017 (the equivalent of one in six).
The Shared Data Unit makes data journalism available to news organisations across the media industry, as part of a partnership between the BBC and the News Media Association. Stories generated by the partnership included:
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Leicester Mercury: Dozens of mobile phones are being discovered inside Leicestershire prisons 17 May 2018
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The Scotsman: Dozens of illegal mobile phones confiscated at HMP Edinburgh 17 May 2018
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ITV Wales: More than 50% of HMP Berwyn prisoners found to have mobile phones 17 May 2018
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Hull Daily Mail: Staggering rise in prisoners caught with phones in HMP Hull, Humber and Full Sutton 17 May 2018
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Liverpool Echo: Liverpool's prisons 'awash' with mobile phones 17 May 2018
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Yorkshire Evening Post: Huge rise in illicit mobile phones in Leeds prison 17 May 2018
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Nottingham Post: More than 100 mobile phones and SIM cards confiscated from HMP Nottingham last year, figures reveal 17 May 2018
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Derby Telegraph: Hundreds of mobile phones found in Derbyshire prisons 17 May 2018
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Gloucestershire Live: Revealed: The enormous increase in prisoners smuggling mobile phones into jail 17 May 2018
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2BR Lancashire: Over '500% rise' in mobile phone discoveries at Preston Prison 17 May 2018
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Spirit FM: Illegal mobiles and SIM cards confiscated from Ford prisoners 17 May 2018
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Scotland: Evening Express: North-east superjail prisoners found with 25 mobiles 17 May 2018
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Wigan Today: Mobile phone seizures at Hindley Prison among highest in UK 17 May 2018
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The News: Winchester jail awash with illegal mobile phones 17 May 2018
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Chronicle Live: Rise in number of mobile phones found in North East prisons - and they could be keeping inmates safe 17 May 2018
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News Post Leader: Hike in number of mobile phones confiscated in Northumberland prison 17 May 2018
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The Lincolnite: Mobile phones increase at Lincoln prison 17 May 2018
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The Star: Doncaster Prison sees 3,350 per cent rise in seizures of mobile phones and SIM cards 17 May 2018
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The Times & Star: Figures released for number of smuggled phones confiscated from Cumbria's prison 17 May 2018
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Morpeth Herald: Hike in number of mobile phones confiscated in Northumberland prison 17 May 2018
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Sunderland Echo: Huge rise in seizures of mobile phones and SIM cards from North East prisoners 17 May 2018
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Northumberland Gazette: Hike in number of mobile phones confiscated in Northumberland prison 17 May 2018
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Northamptonshire Telegraph: Northamptonshire prison gets tough on mobile phone smuggling inmates 18 May 2018
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The Bucks Herald: Aylesbury Prison is one of the worst in Country for mobile phone confiscations 18 May 2018
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The Gazette: Phone shock at Kirkham Prison 18 May 2018
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DnG24: Prison reports low rates of phone smuggling 21 May 2018
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Brighton: The Argus: MP says mobile phones Bill is urgently needed 28 May 2018
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This story was also used by BBC Radio London, Midlands Today, North West Today, BBC Radio Wales, BBC Radio Cornwall, BBC Newcastle, BBC Radio Lincolnshire, BBC Radio Solent, BBC Guernsey, BBC Radio Nottingham, BBC Radio Manchester, BBC Radio Shropshire, BBC Coventry & Warwickshire, BBC Hereford & Worcester
