Parking on my bumper

Hi all. I'm really sorry to jump in and ask a question without introducing myself, but I have a problem that is stopping me getting to work at times. There hasn't been an argument or anything I can point to as to why but my next door neighbours have decided to park their cars either side of mine whenever they can. One of them (this is a mother and son) will pull his car so close to mine that he is literally touching my bumper.

Is this legal?

Thank you in advance.