Fuji is right.
I fly IFR about a third of my time. For flights in UK I have only ever filed a written flight plan once - about nine years ago because another pilot (the TRI) wanted to try flying airways for part of the route. We never got anywhere near our requested route due to ATC reasons.
Since then I tell myself if I am going IFR and plan to fly outside airways. No-one else gets a copy of a written FP because quite frankly, no-one else gives a monkey's so I don't file one. I don't want to practice bleeding or stick pins in my own eyes. If I need an IFR crossing of Class D airspace I ask on the r/t or go around it if they sound too busy.