Not just PIK.
I went through BHX in April with all our liquids in two bags but we were stopped, as the bags were too big and security provided the "correct" ones free of charge. They also spotted my daughter's face cream, which was 200ml although the size was hidden behind a sticky bar code (I hadn't noticed it packed, as it looked more 100ml).
Security were very pleasant and efficient although if they had charged me, I would have asked exactly where on the website it gives the dimensions of the bags - I had checked the night before and I could not find it.
Also I too have got drink through (not on purpose) at non-uk airports without it being spotted.
I never mind being stopped or pulled up about these things as long as it is done politely although the size of a see-through bag is a bit
Pete