House Sparrow sabotaging andkilling House Martin nests

Hi There

Have joined this site just to ask if anybody has any advice on how to stop a house sparrow destroying the nests and killing house martin chicks.

There are about 9 house martins nest around the eves of my house, they return every year, but this seems to be the first year that they have been in danger from another bird.  I came home from work last night to find seven dead chicks lying on the ground.  I have watched the house sparrow's activity for the past 3 hours this morning and he is waiting till the adults leave then going into the nests.  He is working his way along the nests and I am helpless to do anything.  Any advice would be so gratefully appreciated.  Thank You