In the UK it is illegal to remove tadpole or spawn from any pond, even if the pond is in your own backyard.
Our native amphibians are all threatened by destruction of habitat and poisoning from insecticides & fertilizers leeching into ponds from fields.
If you need to get rid of an overabundence of spawn, tadpoles, frogs, toads or newts from your pond, contact a local conservation group and they will relocate them to a safe pond.