Thanks for your question.
As your original lease has ended and have not signed the renewal lease you can potentially serve notice. It will depend if you had a protected tenancy and have been holding over on those terms or had an unprotected tenancy but have been occupying since the end if that tenancy on periodic tenancy terms.
Without further details, sight of documents I cannot comment further on the validity of your notice.
If you have served a valid notice and pay rent up to the end if the notice then the landlord has no claim on the deposit in respect of arrears or loss of Rent.
As for dilapidations, the standard obligation is for full repair. This means that you have to put the property into repair, I.e remedy historical dilapidations unless your lease has a schedule of condition attached and specific wording that you are not required to put it into a better state of repair and condition as evidenced by the schedule. It is one of the extremely unfair terms a tenant is subject to when taking a lease.
Potentially you are liable to repair and remedy historical dilapidations.
Generally the acceptable condition required by landlords is old for new, full renovation back to new condition.
Your deposit can be taken to cover part of any dilapidations claim brought against you.
Do you have any questions or queries?
Happy to assist further.