Thanks for the replies. There are, in many locations, preferred routes. Dependent on how sophisticated the IFPS and/or ATM system is it will flag/reject incorrect routes. ATC holds stored flight plans for scheduled flights, but on the day your company files a slightly different route and the system does not pick it up. Best practice requires ATC to confirm the route step by step. I am used to giving waypoints for my sectors and the first waypoint inside the next sector - and so on through the other sectors within the FIR. As a pilot you can look at your FMS and nav display and instantly confirm that we have the same waypoints/route, or not! But if I say UL423 - how do you instantly check and confirm that UL423 equates to waypoints Alpha, Echo, Oscar etc?