MOTORISTS beware! If you plan to use the M4 over the May bank holiday weekend prepare to get caught in traffic chaos.

Motoring organisation the AA is warning that the combination of sporting events, a music festival, railway engineering works and increased holiday traffic could lead to problems between London and Cardiff.

It is expecting tens of thousands of motorists on the M4 corridor, including about 70,000 Chelsea and Arsenal fans heading for the Millennium Stadium in Cardiff for the FA Cup final on Saturday.

At the same time the Badminton Horse Trials in Gloucestershire - one of the biggest sporting events in the West - is likely to attract some 250,000 visitors. In addition, about 45,000 music fans are expected to visit the Essential Festival - a major three-day music event in Bristol.

An AA spokesman said: "With rail engineering works affecting London, Reading, Newbury and parts of the West Country, many people will be seeking alternative transport for their bank holiday getaway.

"People will feel let down by the public transport network. It's a shame that the engineering work on the railways is happening the same time as major sporting and leisure events along the M4 corridor."

The AA has predicted the M4 rush is likely to last from Friday afternoon to Saturday lunchtime, with two sets of football fans leaving London and all heading in the same direction.

It is encouraging drivers to plan their journey, listen to traffic bulletins, car-share and use park-and-ride systems where possible.

The AA has also reminded fans to stay off the alcohol if they are driving back to London after the match.

"It will be tempting for fans to toast their team's success or to drown their sorrows if they lose. But motorists need to save their celebrations - or commiserations - until they are not getting behind the wheel.