People travelling home for Christmas have been told to expect mist and fog as well as severe delays in some areas.

With half of UK motorists expected to take main roads or motorways on Christmas Eve, analysis by the RAC suggests the busiest period will be between 11am and 1pm.

The worst road for long delays is expected to be the M1 northbound from junction 21 (Coventry/Leicester) to junction 26 (Nottingham/Ripley). The M25, M5, M6 and M40 have also been identified as likely to see significant delays over the festive period.

Highways England lifted more than 200 miles of roadworks on the country’s motorways and major A roads on Friday to ensure more than 97% of its network is open.

Parts of Britain could wake up to mist and fog on Christmas Day, with a cloudy day forecast for most of the country.

The Met Office has already issued yellow weather warnings for fog in Northern Ireland and central and south-west Scotland for dense fog and freezing fog patches.

These run until 10am on Christmas Eve, but Greg Dewhurst, a forecaster, said the warnings could be extended.

“It could be quite dense from this evening and through the night tonight,” he said. “It will be a grey start for most. In the east it will be mostly dry, an odd spot of drizzle is possible in the west.”

Anyone hoping to escape motoring misery by catching a train could also face difficulties. As usual, there will be no trains on Christmas Day and a limited service on Boxing Day.

But some of Network Rail’s 330 Christmas engineering projects have already begun, closing a number of lines. There are no services between London Victoria – the UK’s second-busiest railway station – and Clapham Junction until 2 January due to track renewal.

Crossrail work means there are no trains operating to or from London Paddington on 23 December, Christmas Eve or 30 December, with a reduced service on 27, 28, 29 and 31 December.

This could cause problems for people heading to Heathrow.

Liverpool Lime Street will have a reduced service from Monday until New Year’s Day, affecting Virgin Trains, East Midlands Trains, London Northwestern Railway and Northern.

There are improvement projects at numerous other locations and passengers are urged to check the National Rail Enquiries website before they travel.