The organisation's chairman Eli Katz said in a statement: "“Several Comms Council UK members and international IP-based communications service providers have been subjected to distributed denial of service attacks over the past four weeks which appear to be part of a co-ordinated extortion-focused international campaign by professional cyber criminals."

The companies affected offer calls over the Internet to both private and public customers, including law enforcement and the National Health Service.

One provider, Voipfone UK, indicated that the latest attack had begun on Monday and that similar attacks had been taking place since the end of September.

Katz said the Comms Council was working closely with the UK Government, National Cyber Security Centre, Ofcom and international agencies "to share information and details about the nature of the attacks in the expectation of halting this criminal activity as quickly as possible".

Some Windows ransomware gangs are known to use DDoS attacks as the last option in trying to force their victims to negotiate, after encrypting their files and threats of a data leak have both failed to get a positive response.

"As our members supply telecoms services to critical infrastructure organisations including the police, NHS and other public services, attacks on our members are attacks on the foundations of UK infrastructure.

"We are confident that, with a joined-up government-led initiative, this damaging criminal activity can be halted.“