Engineers are closing the section between Newbury and Hungerford from 7pm Saturday until 9am Sunday, so a bridge for horses can be installed at Bussocks Wood, half a mile west of Junction 13.

The £39 million Chieveley underpass is now just three months from completion, but stretches of the new road system are already in use.

The detour will add seven miles to journeys, but Highways Agency project manager John Martin said: "We need to close the motorway to put up the bridge, but we are doing the work overnight at the weekend to avoid the busy peak times during the week."

"The new bridge will link up to a number of bridleways in the area allowing horse riders to cross the M4 instead of using the Newbury-Wantage road."

Once the work is finished, life for the M4 motorist is unlikely to be dull. On Monday, one lane of the motorway between Swindon and Chippenham will be closed for £2 million of cabling work, while the east Berkshire section is also down for a major upgrade.