It's exactly the same with reptiles...it wouldn't be legal to feed a python a live rat if it would happily feed on defrost. There's absolutely no need, and just creating suffering for the prey animal.
I feed my 2 Ball Pythons small live mice all the time. In fact, if they kill their pray and then move for any reason or lose it, they won't eat the dead mouse. I had to handfeed one of them with small frozen inky mice when I first got it (it refused ot eat anything), but once it started eating regularly, it got switched over to live mice. I used to breed them myself, but one time the power went out in the middle of the winter (ice storm) and there was no backup power supply. The tank temp dropped and they went into hybernation for 6 months (even after I got the tank temp back up to par), that was a treat for me. I had to give all my mice to a lps and havn't bred since as I'm afraid of that happening again.
Also, I feed my Ribbon Snake live feeder fish. I heard that (on many sites, including 3 different reptile forums) that feeding guppies prvide no nutrition to snakes, but Minnows are their natural food source as they are a river snake and close relative to Garter Snakes.
My snakes have never had any ill effects from it to date and really can't imagine them taking dead foods. But that is just me and my opinion. I'm from the US so I know this doesnt apply to across the pond, but I myself only feed live feeder fish as a treat once in a while and only "culls" from livebearer batches or convict spawings. I try to stay away from it, as I've found that it reverts the fish back to a primitive state and all they do is become aggressive to their tankmates when they get fed feeders. That's why I stay as far away as possible.
I want to mention that if you do feel the need to use feeder fish, make sure you quarantine them and use PraziPro. I've seen a lot of feeder fish have ringworms and tapeworms in them that are bigger than the fish. If your fish eats it, well he has it too now. PraziPro will kill them.
I don't like to feed live fish but when I have to I use that and also use it on every new show fish I buy. I know I've said this before but I haven't heard anyone mention to use it before.
I never knew that... I'll have ot look into getting PraziPro. I don't feed live foods to my fish, but I use Rosey Red Minnows to feed my Ribbon Snake and I've quarenteened them first, but never knew of such a product existing, nor the fact of the ringworms and tapeworms. I lways thought reptile digestive systems handle them readily.
That is just my $0.02 in all this.