A cheap and often effective way is to word a letter very formaly -7 days to pay_ and record delivery it so they have to often go to the sorting office to collect (now deliverys are about 10 AM). this lets them know you are serious. and I usually find it works. then its small claims court letter and they usually cave in.
The hassle comes if they have time on their hands/unemployed and counter claim (not happy with job)-you then have to take time off work to defend your claim.
If they have a CCJ already you probably wont get your 250 .
It only happens once a year for us, I get very angry and feel I want to nuke their car, then calm down and weigh up if its worth it and hope justice will be done ( i.e they get leprosy )good luck
Barry