Can you settle an argument for me?

[tahmelapachme33]

Apparently along with the tanker driver strikes, some Geordie farmer is arranging for trucks to block the motorway so the army cant get through driving the petrol tankers. This is the argument, I say no one can block motorways (except the emergency services and highway agency), my friend says they can as there is no one to stop them. How exactly can people block a motorway, wont the blockers be arrested before or during, and wont the farmer be arrested to for some Sect 5 public order or some traffic law?