Passengers face more airport chaos next week when cabin baggage rules change yet again. Fluids are to be allowed on flights leaving British airports for the first time in 13 weeks under new Europe-wide rules to take effect next Monday. "Once the official announcement is made, we're expecting bedlam," said a senior airport official.

A total ban on cabin baggage at British airports came into effect on 10 August in response to an alleged terrorist plot to blow up US-bound aircraft. The prohibition placed huge strains on security staff and baggage systems, and led to gridlock at Heathrow, Gatwick and Stansted. Hundreds of flights were cancelled, hundreds of thousands of journeys were delayed or abandoned, and airlines are believed to have lost close to £100m.

Cabin-baggage rules have been gradually relaxed since then, sometimes causing yet more confusion. When the Department for Transport announced early on 13 August that a small bag would be allowed through checkpoints, airports and airlines were taken by surprise. BAA, which operates Heathrow, Gatwick and Stansted, refused to allow cabin baggage for a further 24 hours.

Uncertainty and disruption continues, with the latest change in rules taking place just 19 days ago. BAA prescribes different maximum dimensions for cabin baggage at different UK airports because, it says, airlines impose their own rules. Over the half-term holiday, Ryanair cancelled some flights to and from Stansted because passengers were stuck in long queues for security.

Staff at the central search area say the main problem is that travellers still turn up with banned items. Rules on the dimensions and contents of cabin baggage have, for BA passengers, changed six times since the end of July.

From 6 November, liquids, pastes and cosmetics will be allowed through the security checkpoints in quantities of up to 100ml (about one-fifth of a pint), providing they are carried in a clear plastic bag with a maximum capacity of one litre.

At present, the UK imposes far stricter rules than countries on the Continent, although there are some absurd local exceptions: German airports currently allow liquids on European flights - except morning departures from Frankfurt. Although the new rules set a minimum standard, individual authorities will have the option to be more restrictive.

The change represents a tightening of rules for every European country except Britain, where it loosens the present no-liquids policy. Airport officials fear two repercussions. This week, some travellers will assume that the relaxed rules are already in effect, and turn up with prohibited fluids. And after Monday, many passengers are expected to carry more through the central search area, which will increase processing times, leading to longer queues and more delayed or missed flights.

What you can take on board


* One item of cabin baggage, with maximum dimensions of 56cm x 45cm x 25cm. Musical instruments, pushchairs, wheelchairs and walking aids are permitted, but will be screened.

* Essential medicines for the flight (liquid and solid), so long as they are verified as authentic.

* Baby milk and liquid baby food - contents must be tasted by accompanying passenger.

From 6 November

* Liquids, gels, pastes and aerosols, including water, soft drinks, toiletries and cosmetics, in containers of 100ml or less can be taken on board.

* The containers must be carried in a resealable, transparent plastic bag with a maximum volume of one litre. Passengers are limited to one plastic bag each, and bags must be presented separately during luggage inspection.