Serve Notice on new contract

A tenant moved out of our property we rent, so we gave the ones left a new 6 months contract. This was a month ago. We now want to move back into the property. Covid regulations now require 6 months notice. Can we give them 6 months notice from now using a Section 21 or do we have to wait until the 4 months is up before we give them 6 months notice?

As the tenants are not the same as the previous tenancy, this would not be a replacement tenancy but a whole new tenancy. Therefore you would have to wait until day 1 of month 5 until you can serve a s21 notice. If the tenants refuse to leave, you should not rely on getting possession for a couple of years from now so you should probably make alternative arrangements for your own accommodation.