A total of 12 people have been arrested during the fuel protest on the M4, police have confirmed.
All were arrested for breaching the legal notice issued by police prior to the protest by driving under 30mph for "a prolonged amount of time".
The protest over fuel prices, which brought parts of the M4 to a standstill, started at around 7:00am this morning (July 4). At 8.30am, four people were arrested with a further eight at around 10:45am.
Gwent Police said it had been working with protest organisers over the past couple of weeks to ensure it was conducted safely.
However, against the arranged agreement, the Prince of Wales bridge was blocked and protestors drove under 30mph.
Chief Superintendent, Tom Harding, explained: "Over the last two weeks, we have been working jointly with a number of partners to ensure that emergency and critical services could continue and to prevent serious disruption to both road users and local communities.
"The right to protest under UK law must be balanced with the rights of the wider community who may be affected. By implementing restrictions on the moving protest, we aimed to protect the public and local communities.
"Along with partners, we identified that failing to comply with the legal notice requirements would lead to emergency and critical services being restricted therefore posing a risk to local communities, action was taken when I deemed these risks existed.
"We are aware of other driving offences, not connected to the protest, such as the use of a mobile phone whilst driving. These offences will be dealt with appropriately", he added.
Police previously warned of "serious disruption throughout the day" as protesters target motorways in a demonstration over high fuel prices.
The east and westbound carriageways of the Prince of Wales bridge have been closed due to the protest, with queueing traffic between J21 M48 and J22 M49.
Around 100 police officers were on the westbound carriageway. It is understood that protesters who had blocked the eastbound carriageway of the Severn crossing were also being arrested.
Gwent Police warned protesters that it was aware of "driving offences" being committed during the fuel protest: "We are committed to increasing the safety of all road users in Gwent and beyond.
"We urge all motorists to drive carefully, responsibly and within the limits of the law."
A number of the M4 protesters have said they believe those who were arrested have been “unfairly” targeted by Gwent Police and Avon and Somerset Police.
Drivers of the vehicles conducting a rolling roadblock on the motorway from Magor Services this morning were arrested for a public order offence, breaching the rules requiring them to drive at a speed of 30mph or more.
Passengers of some of the vehicles, who were driven back to the service station in a police van just before midday, said some of the motorists were unable to drive any faster due to the demonstrators leading the convoy driving at about 10-15mph.
Some motorists were out of their cars and some were spotted playing football, even though is illegal to do so.
Motorways are subject to specific traffic laws set out by The Motorways Traffic (England and Wales) Regulations 1982.
These make it illegal, for instance, to walk on a motorway, and govern where drivers are allowed to enter the roads, and how they must behave once they are on them.
Officers from both Gwent Police and Avon and Somerset Police are in attendance at the protest to ensure it is carried out in line with the law.
Plans are also being made with emergency and critical services to reduce disruption, and Bristol Airport has issued a warning urging travellers to allow extra time if heading to or from the airport.
Protests across the UK will target mainly three-lane motorways and could see slow-downs on two lanes, leaving the fast lane free, according to FairFuelUK founder Howard Cox.
While he said his organisation is not involved in the action, he is "fully supportive" of the demonstrations so long as they are conducted legally.
Chancellor Rishi Sunak has said he will carefully consider calls for a "more substantial" fuel duty cut after the 5p per litre reduction implemented in March failed to halt price rises.
Figures from data firm Experian show the average price of a litre of petrol at UK forecourts reached a new high of 191.4p on Thursday, while diesel rose to 199.1p.
The UK Government said while it understands people are struggling with rising prices and have a right to protest, "people's day-to-day lives should not be disrupted" and warned that traffic delays "will only add to fuel use".