@Trashtara
The no contract is a red herring - you did have a contract, a 6 months one and it then became a statutory periodic rolling contract. This is the default by law.
As Sargass08 as long as you ended the tenancy correctly - 1 month in writing ending on the first or last day of the tenancy period then you are not liable for more rent.
If you did not end the tenancy correctly then you are liable for rent.
They could take you to court. The judge could look on you favourably with regards to the lost rent being fair payment for the lack of gas safety check etc OR the judge could order you to pay the rent AND then deal with their breach of landlord regulations.
Two wrongs do not make a right and the law with regards to rent is quite clear - you pay it, no matter what.
Correct but you can't keep charging someone rent infinitely because of a technicality. After more than 1 month, the landlord won't have suffered any losses because of the OP giving notice incorrectly (if she didn't), assuming the landlord has accepted the keys back and knows OP has left. If the property has been relet, the landlord would have no claim at all from the date it was relet. Given there is no record of the rent, the landlord is going to find it very hard to make a case anyway.
@NoMoreMarbles0 on what grounds are they saying you owe rent?
Did you give notice correctly?
If you didn't, did the landlord write to you that at the time to say you hadn't given notice correctly, that they don't accept your notice and advise you how to give notice correctly? They can't accept the keys back, let you move out and then tell you that you didn't give notice correctly so have to pay rent.
Does your contract state that when the fixed term expires your tenancy will become a periodic tenancy if you don't agree a new fixed term and explain how to give notice on a periodic tenancy? It doesn't mean that it isn't a periodic tenancy but it would count against the landlord if they have never told you how to give notice correctly (as above).
Have they made any formal demands for rent in writing since you left the property?
As for the gas safety record, you must report them to the HSE. It is a criminal offence to let a property without a gas safety record with fines of up to £6k or 6 months imprisonment.
www.hse.gov.uk/gas/domestic/faqtenant.htm
You should also report them to the council for removing the smoke alarms, as well as the gas safety certificate. It won't be easy as many councils no longer have a private tenancy relations officer. If they don't, contact the environmental health department. The council can prosecute bad landlords and the courts can issue banning orders so they cannot let property.
england.shelter.org.uk/housing_advice/repairs/fire_safety_advice_for_tenants
I would ask the landlord exactly what they mean by "things getting ugly". It sounds like a veiled threat to me. If they do make threats, you should report them to the police and the council (as above). If they are convicted of harassment (the council can prosecute, even if the police don't), you may be able to get a rent repayment order for up to 12 months rent.
Regardless of what happens with their claim for rent, I would urge you to go ahead with reporting them about the other issues because they are so serious. Eleven years with no gas safety checks is shocking 