Smut fans were so incensed about the poor quality of the porn DVDs they had purchased from a black-market merchant that they complained to Trading Standards.

Customers of Fantasy Dome in Hull contacted consumer watchdog officials because there was not enough filth on the films made by former sex shop owner Fred Thompson, 69, and his three accomplices.

Blue movie afficiendos also complained that the XXX films were too short and the image quality was poor.

The nature of the sexually explicit material often meant that dissatisfied customers were too embarrassed to complain, lawyers at Hull Crown Court said, but some clients of Fantasy Dome overcame their shame enough to lodge official complaints.

It emerged in court that Fantasy Dome was a scam operation which sold knock-off versions of existing titles. DVD covers and inlay sleeves were also created at the gang's Beverley Road headquarters.

Pensioner Thompson, along with Shaun Langley, Nigel Maw, 52, and David Maw, 31, were found guilty of running the operation. All now face prison.

Charlene Summall, prosecuting, said: "All four defendants played individual and key roles in this agreement to produce, distribute, defraud and encourage the sale of adult content material.

"All the material found, save for a few original discs, have been found to be illicit.

"A large DVD rewriter was able to produce four copies of a DVD at the same time.

"Unsuspecting members of the public were in no position to complain to Trading Standards that they were getting shoddy discs because of the nature of the product."

As well as illegal porn DVDs, police officers also a banknote printing press, which the gang used to pump £22,000 in counterfeit currency into the local economy.

Judge Mark Bury told the gang: "You have all been convicted and I will adjourn sentence. You can all have bail in the meantime.

"These are serious offences for which a sentence of imprisonment may well be passed."