After years of pressure from the government, America's television industry yesterday announced the first ever classi- fication system for its programmes. But even before it was unveiled, critics insisted the new scheme was too lax to be effective.

The voluntary code, which will take effect in the next two months, is closely modelled on the existing classification system for films. Six categories will apply to all entertainment programmes, ranging from "TV- G", or suitable for all ages, to "TV-M", for people aged 17 and over. All children's programmes will be labelled either "TV-Y", suitable for all children, or "TV-Y-7", recommended for children aged seven or more.

The logo will appear in television listings and guides, and be shown for 15 seconds in the top left-hand corner of the screen at the start of each programme. It will be repeated during programmes lasting an hour or longer, only news and sport will be exempt.

The guidelines however were instantly denounced by children's advocacy groups, who argue they are far too vague on a programme's contents. Unlike film classifications, set by an independent body, the TV categories will be decided by the TV companies themselves - a process critics liken to putting a fox in charge of the chicken-coop.

Parents' organisations are demanding specific gradings for sex, violence and bad language. "What parent in their right mind would accept a package at the front door labelled `suitable for a 10-year-old' and hand it to a child without further inspection?" asked Gary Bauer, head of the conservative Family Research Council.

But Jack Valenti, President of the Motion Picture Association of America, said the industry would only accept its own voluntary system, and would fight any alternative in the courts.