A British man who plotted to kidnap, rape, murder and eat a child – and had prepared a dungeon apparently for use in the grisly ritual – faces up to 27 years in a US jail before deportation to the UK under a plea agreement.

Geoffrey Portway, 40, who had been living in Worcester, Massachusetts, has admitted "solicitation to commit a crime of violence" and distributing and possessing child abuse images.

The details were revealed under a statement released by the US attorney's office in Boston. It said that Portway had engaged in "numerous online chats with many individuals" about a mutual interest in abducting and murdering children and exchanged child abuse images.

Federal agents, state and local police seized computers, digital equipment and images while executing a search warrant at Portway's home last summer, and also found a dungeon in the basement behind two locked doors.

The room, was lined with sound-muffling equipment as well as a chair, television, and what appeared to be cable access to the internet. It also contained a child-sized homemade coffin with large speakers covered in wire mesh at one end and exterior locking devices, a steel cage with multiple locking devices, and a steel table top with steel rings at six points, presumably for restraints, said the statement.

They also found freezers, disposable scalpels, butchering kits and castration tools at the property.

"The dungeon was described in detail by Portway in recovered chats as a place he intended to use to keep kidnapped children while he sexually abused them and as a place to eventually murder and cannibalise the children", said the statement.

Since at least 2010, Portway had used Skype and other programmes to communicate with a man called Michael Arnett, from Kansas, trading images of injured, mutilated and dead children and chatting about sexual abuse, rape, abduction, murder and cannibalisation of children.

Portway had "repeatedly solicited Arnett to kidnap a child for him, with the intent that Portway would ultimately rape, kill and eat that child".

The attorney's office said: "These solicitations for help abducting a child included discussing real children, by name and photo, that Arnett claimed to know and have access. In the chats, Portway and Arnett discuss different ways to kidnap children and the age range that Portway prefers.

"During the time that Portway was soliciting Arnett, Portway had been told that Arnett had helped others with such requests before and that Arnett had experience with the abduction and sexual abuse of children."

Arnett had since pleaded guilty in Kansas to the sexual exploitation of a child for the purposes of producing child abuse images. Examination of computers also revealed more than 4,500 trades of child abuse images between Portway and others.

US attorney Carmen Ortiz said: "I hope that this case sends a clear message that we will prosecute to the fullest extent of the law those who participate in these types of activities. Even though criminals attempt to hide in the anonymity provided by the internet, the department of justice is committed to aggressively pursuing them to ensure that there is no place to hide."

Portway is said by authorities to be part of a worldwide network of offenders. Agents from homeland security investigations said they have been able to rescue 160 children and arrest 51 perpetrators since a man called Robert Diduca was arrested on child abuse-related charges in Milford, Massachusetts, in 2010. He was sentenced to 18 years in June last year.

Bruce Foucart, special agent in charge of HSI Boston, said Portway's guilty plea should serve as a warning to those inclined to abuse children or share images of child pornography. "There isn't a place in the United States, on the internet, or the planet in which you are truly safe. We will investigate you, we will prosecute you and we will bring you to justice."

Under the terms of the plea agreement, Portway faces 216–327 months in prison in the US and a lifetime supervised release. He will also be required to register as a sex offender. He will deported after serving his sentence.