Wiltshire Police are on high alert along the M4 this week as delegates, including US President Barack Obama, make their way to and from Swindon for the Nato summit in Newport under threat of disruption from activists.

A massive security operation is under way, stretching from Swindon to Swansea, to secure the 230-mile route to the two-day conference and protect the largest number of world leaders to visit Britain at one time.

The sheer number of delegates – there are 28 Nato member states and 39 partner countries, each sending about 30 people – and their respective demands has meant hotels in Newport and Cardiff have been unable to cater for everyone.

Delegates are expected in Swindon throughout the week, with the M4 seen as the ideal route in and out of Celtic Manor resort, but police are anticipating protests and disruption along the motorway.

A Wiltshire Police spokesman said: “Wiltshire Police will be providing support to the policing element of the Nato summit in September.

“These resources are in addition to officers being sent in conjunction with Gloucestershire Constabulary and Avon & Somerset Police as part of the Tri-Force agreements.”

Gwent Police is co-ordinating the operation for the summit on Thursday and Friday.

A spokesman said: “As part of the Nato summit policing operation, Wiltshire, like every police force in the UK, will provide support and mutual aid officers to assist in one of the largest ever UK policing operations.

“We have previously confirmed that over 8,000 mutual aid officers will assist officers from Gwent and South Wales Police to provide safety and security for the summit, which has an operational footprint which extends from Swindon in the east to Swansea in the west.

“For operational reasons we won’t break down how many officers are being deployed from respective forces and the specific roles they are contributing.

“However, officer deployments are co-ordinated nationally to ensure that every force is able to ensure day-to-day policing of their respective areas is unaffected by any NATO summit commitments.

“Policing of the M4 is an important part of the operation and appropriate safety and security planning has been undertaken to ensure the road remains open during the summit and any disruption to the public is minimised.”

Adam Flint, the general manager at the Swindon Marriott Hotel, was approached by agents last September for bookings throughout the week of the summit, but no firm reservations materialised.

He said he was not aware of delegates staying in Swindon, but knew the town had been looked at as an option for those struggling for space in Wales.

“We have got no one on our books coming in,” he said.

“If I have got the odd person coming, I wouldn’t know them from Adam.

"The agents told us they initially wanted 60 rooms across five nights, but when we came to ask for a fee they failed to come back, so we released the rooms in April, if not before.”

Steve Jones, the general manager at Cotswold Water Park Four Pillars Hotel, said they had no delegates staying at their hotel.

Hilton Swindon would neither confirm nor deny any delegates would be staying there.