It is relatively easy to intercept conversations on mobile telephones. Scanning devices can be bought from retail electronic shops.
Eavesdropping mobile phone conversations in the UK is not illegal, although unauthorized publication of the information is as a result of copyright in the spoken word if recorded. Either party to the tapes of recorded conversations in 1991 of the Prince and Princess of Wales could have applied for an injunction to stop publication (but to do so would have involved admitting the tapes were genuine).