I am very lucky that I have been breastfeeding for the last 8 months so my milk is ready for use and no tasting required at security!!! speaking about BAA at LGW, they never asked me to open any sealed fruit pots for my baby.
They did ask me to taste the boiled water though, which I always keep in a bottle in my bag in case he gets thirsty.
Boots sell all sorts of baby food airside. However, the most economical way of doing it is this:
Fill up 3-4 bootles, how many you need, with the water ready for the formula powder. Then get one of this:
http://www.jojomamanbebe.co.uk/detai...category=ABB72
it can contain up to 4 x 7oz powder formula doses. All you have to do is show them you can taste the water, seal the bottle again and when you need it just add the content of one formula compartment, shake, heat (or not, depending what your baby is used to) and feed!!! I personally would provide my own water and would not ask the crew for hot water on the plane, as the quality of it is debatable, especially for a little baby (being crew myself I can assure you it's not sterile at all!)
This way, although we could argue that you could "contaminate" the water when you taste it (which would be like kissing your baby though if you know what I mean), you can quickly make a fresh feed each time.
Good luck!!!!!
FBW