French Law on evicting tenants, help needed please

Hi
My friend (English, living in UK)is having trouble with tenants (also English)in his French house, whose tenancy has now ended, but they have not left/appear to not be going to leave. My friend had the water turned of yesterday and now his wife is getting abusive calls from the tenant.
Can my friend just go over and evict them ?
Is there a short legal way, or could it be a long protracted/expensive process ?
Thanks