Unfortunately, this is a growing issue in the UK as we have little on-road parking, narrow roads and an increasing number of cars. I would speak to the owners again and tell them you plan to get the council and possibly the police involved as it's an obstruction to block a dropped kerb and to keep you from accessing/exiting your own property. The first step with any anti-social parking problem is to contact your local authority and/or the police on their non-emergency number. However, there is little the law can do to support homeowners in this situation as it's a civil matter rather than criminal.

In some circumstances, the local authority can take civil enforcement action if a vehicle is parked in front of a dropped kerb so it would be advisable to contact them. If it were me, I'd also take photos of the cars blocking your driveway as proof. Another option is to pursue a legal claim for nuisance on the grounds that the driver is interfering with your use and enjoyment of your property – but to do so you’d need to know the identity of the offending vehicle’s owner. If you get nowhere with the council and the police, I'd try Citizens Advice last.