Pro-Brexit campaigners have been prosecuted for inconsiderate driving while trying to bring roads to a standstill.

According to organisers, the demonstrations aimed to ensure the UK leaves the EU on 29 March by causing gridlock on motorways and A-roads using a convoy of slow-moving vehicles.

The protesters were aiming to target between 30 and 40 locations over the weekend, including the M25, M6 and M1.

Devon and Cornwall police said the lead drivers of convoys on the A30 and M5 were stopped and prosecuted for careless and inconsiderate driving.

The force said it had spoken to organisers of both protests beforehand and told them they were to ensure other motorists could pass them and not drop down to unsafe speeds.

Inspector Simon Jenkinson said the force was “happy to facilitate” the protests as long as they did not bring roads to a standstill.

But he said campaigners had blocked both lanes of the A30 towards Cornwall and at least two lanes of the M5 northbound while travelling at speeds as low as 20mph on the motorway. “That presents a significant risk on a very busy arterial road.”

Highways England tweeted: “There have been a few issues but nothing of any major impact and at present everything is running as usual.”

The organiser of the protests, Ian Charlesworth, 55, said: “The ultimate aim is to make sure come hell or high water that Britain leaves on March 29.” But he was unsure how effective they would be.