I may be remembering wrong, but i think it is legal. It´s not, however, something i would recommend and although i can´t remember, it may well be illegal to release them.
I understand you want to help, and this seems like a good way of doing it, but it could be problematic and it won´t necessarily produce any benefits. By taking them home you might expose them to pathogens which would then be released.
Personally i would encourage you to do something about the drying pond, if at all possible, or perhaps create new habitats. That´s the best help of all. Moving animals around is not ideal...
Also, i know it seems somewhat crash, but being explosive breeders, newts are very good at recovering from bad years. If this one puddle is drying up this year, it´s hugely unlikely to make any significant impact on local newt numbers.
