The clear sealable bag I used during my Xmas / New Year trip - going through Calgary, Edmonton, Gatwick, Edinburgh, Aberdeen and Memmingen airports at various stages - was issued sometime in the past at a Canadian Airport, as it has the Canadian Govt logo on it and refers to the 100ml restrictions etc. Therefore it would appear to be be some sort of "officially sanctioned" bag?
However when going through security at Edinburgh airport, a member of staff there was very concerned about it as it was "non compliant" as it is a rectangular shape (fairly small in size, don't have it to hand right now), and she handed me a square-shaped bag and asked me to use it in future.
No other airport from the list above queried my rectangular bag - not quite sure what the issue was at Edinburgh?
Mind you, another member of staff at Edinburgh was insistent that my hooded sweatshirt had to be taken off, as it was a "jacket"?!