Yes, It would probably put them out, dropping the appointmant at 2 mins notice, however I phoned as soon as the surgery was open(an hour before my appointment). I couldn't phone any earlier, they aren't open on the weekend.
It is true that I could take my business elsewhere, but I have been seeing this GP for 14 years and we have an excellent dr-patient relationship.He has delivered 3 of my children. The receptionist is new and I have to say, I have noticed she isn't very good at her job, she is often flustered and doesn't seem to know what to do. But, again, it doesn't excuse rudeness.
Frankly, the time it took to write the letter of complaint, was alot less time than I spend on Mumsnet, so it wasn't a big deal.
As I said earlier, I will speak to the doctor about it rather than sending a letter, writing it meant I got it off my chest and didn't lose any sleep over it.
For the poster who thought it wasn't rude, I still think it was, she spoke to me with a condescending tone and implied I had wasted their time intentionally.I suppose I didn't say that in the original post, but it was as much her tone as the words used.
Incidentally, when I cancelled the appointment a different receptionist spoke to me and thanked me for calling and cancelling.
Thanks everyone for your input.