I went to main dealer and it was steep, I had a letter for 20% off though, came in post, then at 36k I just asked for 10% off since they had given a discount before and girl said no problem and when I was in other people were booking in and asking, when I then went to drop car off they confirmed, 36k service and 10% off.
Worth doing, (that was Arnold Clark btw), just say you had a discount before, could they do 10% again or something.