The tunnel should not have been dug in a conservation area. It will disturb small animals and historically important stuff. The perpetrators should be prosecuted and probably sentenced to hard labour on a major infrastructure project.
Will there be any effect on the 'real' project, I doubt it, applause from their supporters maybe.
I really don't support HS2 as it seems to be a money making scheme for friends of the decision makers, but dangerous little protests will make difference what so ever.