Superintendent Michael Hames of the Obscene Publications Squad said two developments had made hard-core pornography more freely and legally available.
'It's now possible to get the kind of porn we would normally expect to seize, beamed directly into people's homes via satellite and we can't do anything about it. And it's also possible to get scenes, which again would normally spark off police action, in videos which are marketed under an 'educational' label and available in W H Smith and other high street shops.'
He predicted that defendants accused of selling pornographic videos would soon be telling the courts: 'Why pick on me? You can tune into this stuff on your television at home.'
The hard-core pornography is being beamed into British homes via European satellite stations. Such material would be illegal if sold over the counter in Britain, but a European Community agreement allows Britons to receive the transmissions if they are legal in the country of origin.
The British Board of Film Classification says that as British tests of obscenity are the strictest in Europe, it is inevitable that some sex material originating in European countries will be stronger than what is allowed here.
Supt Hames said that satellite transmissions contained scenes of fellatio and sexual intercourse that would be illegal if sold on video in Britain.
'The crazy thing is that if someone tuned in and ran off a video of the programme to hand over to a friend, then he or she would be committing an offence under the 1959 Obscene Publications Act.'
He said that in the past few months, he had examined several sex education videos aimed at the heterosexual and homosexual markets. In some cases there were scenes that would normally be illegal.
'In each case, the British Board of Film Classification passed the video because the educational element justified an exemption under the 1959 Act,' Supt Hames said.
But some were being marketed in the same manner as pornographic titles.
'One was advertised as Hot Sex Now, words which seem to be concerned with titillation rather than education. When we examined one 'educational' video we found someone putting a condom on an erect penis.
'While encouraging the use of condoms is sensible, I wonder if it's essential to lingeringly depict an erect penis to show how it's done.'
Supt Hames said he was not arguing for those videos to be banned, but for a greater clarification in what was obscene and what was not, so he knew what targets his officers should be pursuing.
'It's only a matter of time before hard-core porn professionals use these anomalies in their courtroom defence. The law is an ass in this area.
'I'd like the Government to say whether heterosexual or homosexual sex is now permissible in videos. They should show where the line is to be drawn,' he said.
James Ferman, director of the British Board of Film Classification, said: 'The 'deprave and corrupt' test has always depended on context. These educational sex videos have discreet covers and are marketed discreetly - not like porn videos at all.
'We have the strictest standards in Europe. However, things are changing so quickly that I cannot predict what Parliament will do. But I expect that ministers will be asked questions about this when Parliament resumes.'