UK-France trains hit by heatwave

"It's a very busy day, it's the day when everyone leaves on holiday," a said a spokesman for Eurotunnel, which operates a drive-on train service for cars and trucks going through the Channel Tunnel.

"We are in a heatwave, and added to this is the problem of air conditioning in our shuttles."

The Channel Tunnel runs for 50 kilometres (30 miles) between Kent in southeast England and northern France. Opened in 1994, it is the world's longest uninterrupted undersea link.

"The high temperatures are affecting the operation of air conditioning on our trains resulting (in) delays. We recommend you stock up with drinking water before you arrive," Eurotunnel said on its Twitter account.

The hottest temperatures of the year in Britain were recorded on Thursday. The mercury hit 35.1 degrees Celsius in Wisley on the southwest edge of London.

On Thursday, Eurotunnel delays hit four to five hours.

On Friday, "we are at around one hour and 30 minutes, only on the British side. This is because all the shuttles are in service," the spokesman said.

Different services run through the Channel Tunnel: Eurostar passenger trains, Eurotunnel vehicle shuttles and goods trains.