You do not have to move out on expiry of the notice though. The landlord can only evict you if he has a court order. If you are still in the property upon the expiry of the notice, he will have to apply to court. The process may take further few months.
If the landlord harasses you or threatens you- he may be committing a civil and criminal offence of illegal eviction.
Speak to the council- you are now very possibly "homeless or threatened with homelessness".
Keep lines of communication open with the l/lord; say that he is likely to save himself an awful lot of trouble if he lets you stay for another month to find another property, instead of applying to court.
Additionally, check whether your deposit should have been protected by TDS; if it should and it wasn't- S21 notice cannot be used, although in cases of non-payment of rent a l/lord may have gone for another type of notice.
Check:
Shorthold Tenancy - posession, eviction and notice Revised Homelessness code of guidance for local authorities, July 2006 Tenancy Deposit Scheme
Speak to Shelter
Great links; housing and associated. to confirm all this because you are subletting, you are not actual tenant.