Swallow nest removal

Can somebody give me some advice urgently please? My neighbour has a swallow nest in his eaves with young in it at the moment. He is now replacing woodwork round his house with upvc cladding. I have told him he cant remove the nest whilst young still in it but he insists it is going to be knocked down to allow work to continue. I have tried the "against the law" "wood can stay until young out of nest" etc etc to no avail. Workmen are there at the moment and I have said I will report them if they knock down the nest but its too late then for the young. ADVICE ON MY NEXT MOVE PLEASE>