A Tokyo firm of private detectives is selling off-the-shelf forensic kits to women who want to catch their men out.

The women are sold a special chemical spray which highlights traces of semen in their spouse's underwear.

Called "S-check", the chemicals are supplied in two aerosol cans. Each of them is sprayed on the suspect underwear in turn.

If traces of seminal fluid are present, the second spray turns it bright green.

Detective agency

The method is thought to be similar to the test most commonly used by British forensic scientists.

But a spokeswoman from the Gull Detective Agency said: "I don't know if this is the same type of spray the police use. I'm not allowed to tell you what the chemicals are."

The test relies on the fact that semen is released from the urinary tract for up two hours after ejaculation.

The kits are also being sold by a detective agency in Osaka, and company president Takeshi Makino said he is selling 200 a month.

Mr Makino said 99% of the people buying the Y35,000 (�175) kit were married women.

'Infidelity detection cream'

The Gull Agency also sells a gel which a women rubs into her partner's back before he goes to work.

If he has a shower during the day - seen as a telltale sign of an office affair in Japan - the gel reacts with the water to form a give-away blister.

The agency says the same gel is also temperature sensitive. Rubbed into a man's socks, it will change the colour of the fabric if the socks are taken off for longer than 15 minutes.

Staff refused to reveal the gel's composition, saying only that it is called "infidelity detection cream".

But the potential for catching innocent men is very real.