I'll never forget the look of horror on the face of the young customs lady at Larnaka airport once when she (from quite a distance away) pointed to the bulge coming from my beltline and indicated she wanted me to lift my top to show her what was going on. Once she reaslied it was a Stoma bag, she very quickly turned her head (as did most of the other passengers!)
Instances like that though are rare, and in general you should have no trouble travelling with a stoma - whenever here in the UK or abroad.
I have listed 10 "helpful hints" to follow when travelling. Please let me know if you have any more to suggest.