Non resident parks his 1 sometimes 2 cars here 24/7

There are 2 cars 1 green/1 red parked in our cul de sac 24/7. The owner does not reside in Newton Grove. Sometimes both cars are parked there, sometimes just 1. Parking for the residents is a premium with most flats having 2 cars. Sometimes residents have to park round on Newton Green. The parking here is signposted for residents only and these cars could do with parking at their owners residence to be fair to everyone here. This has been going on for well over a year and the cars are normally parked, per photo, outside number 6 Newton Grove, CM6.