It is definitely illegal as it contravenes the Highways Act 1980. You can take pictures and report it to the council. They can potentially receive a fine and/or be prosecuted. I've had the same experience on my road where parking is limited due to the number of driveways. I've moved them out the way and parked there if necessary and left notes to say it is illegal. However if I do continue to experience this problem, I will be reporting it and taking next steps. Hope this helps!