Drivers are being warned over long delays on major routes as 17.6 million getaway trips by car are expected to take place in the UK over the August bank holiday period.

The RAC, which issued the alert, urged drivers to set off as early as possible or "be prepared to spend longer in traffic".

The South East and South West are expected to have some of the worst congestion.

Some 3.0 million journeys for holidays or day trips are expected to be made on Friday by drivers looking to make the most of the last long weekend before Christmas in England, Wales and Northern Ireland, the RAC said.

This rises to 3.4 million on Saturday, 2.4 million on Sunday and 2.7 million on Monday.

The RAC said an additional 6.1 million drivers are planning a leisure trip at some point between Friday and Monday.

The figures are based on responses to a survey of 2,080 UK adults, extrapolated to the 34 million cars licensed in the UK.

Transport analytics company Inrix predicted the M5 between Bristol and Devon will have the most severe getaway traffic, with the stretch from junction 15 north of Bristol to junction 23 for Bridgwater likely to see delays of more than 40 minutes on Friday and Saturday.

Hold-ups exceeding half an hour are forecast on Friday on the M20 in Kent, which is a route taken by a large proportion of vehicles making Channel crossings via Dover or Folkestone.

The warning relates to journeys from junction 7 near Maidstone to junction 3 (Addington Interchange), and from junction 1 at Swanley to junction 5 at Aylesford.

RAC mobile servicing and repairs team leader Nick Mullender said: "With this bank holiday being the last opportunity to enjoy a long weekend before Christmas, our study shows a real eagerness to get out and about with nearly 18 million drivers planning getaway trips.

"More traffic on the roads will inevitably lead to more vehicle breakdowns, especially if the sun makes an appearance and people decide on the day to visit popular destinations.

"We're expecting major roads to airports and coastal destinations to be extremely busy, especially the south-east and south-west regions which could end up bearing the brunt of most holiday hold-ups.

"Anyone planning routes through these areas should set off as early as possible or be prepared to spend longer in traffic."

Meanwhile, rail passengers are being warned that some major routes will be closed for engineering work as Network Rail conducts 261 projects across Britain.

There will be no long-distance services between London King's Cross and Peterborough on Sunday, disrupting Anglo-Scottish journeys by LNER and Lumo on the East Coast Main Line.

Avanti West Coast will operate a reduced and amended service to and from London Euston.

No services will operate between Birmingham New Street and Birmingham International between Saturday and Monday.

Affected Avanti West Coast and CrossCountry services will be diverted, extending journey times, while London Northwestern services will run to and from Birmingham International only.

Helen Hamlin, Network Rail's chief network operator, said: "With the August bank holiday weekend approaching, we've carefully planned our engineering work to minimise disruption, allowing people to rely on the railway and make the most of the late summer bank holiday weekend.

"While the vast majority of the railway will be running, works on some parts of the network are unfortunately unavoidable, as we complete major work to support a better, more reliable railway that we wouldn't be able to complete in a normal weekend.

"So we're asking passengers to check their journeys in advance to ensure their route isn't affected."