Unsigned Tenancy Agreement

Tenancy Types and Management

I have a property some distance way from where I actually live.
My tenent has been there for about 3 years and each time we wanted to re-new the tenancy, I would put two copies of the new agreement in the post and she would sign and copy and return it and keep one for her own records.

Last year, for some reason, she failed to sign and return a copy to me. Unfortunately, I also forgot about it and am now in the position that I have served s.21 Notice and will need to take possession proceedings.

Where do I stand with the unsigned tenancy agreement? Is it still vaild through her actions, i.e it is signed due to her conduct, or is it invalid as it is not signed yet?

If regarded as invalid, will I have re-serve s.21 Notice?

The other problem I have, is then what happends if later on, she signs her copy and presents it as a valid tenancy agreement?

Any help would be welcome.

Thanks