Not every agreement must be in writing to be enforced. It is just more difficult to prove that there is in fact an agreement or mutual understanding.....for example if there is a witness (preferably a non related person) willing to testify that there was as agreement or a security deposit receipt or monthly rental receipts or bank statement.

If the tenant dispute that there is no TA, then he is consider an 'illegal occupier". He cant be living in the property without the 'consent' (verbal agreement) of the 'landlord' in the first place.

What can the landlord do in respect of an illegal occupier ? .....

1. Give notice to vacate;
2. Lodge a police report;
3. Disconnect utilities supply;
4. Lock up the property (Ensure no occupier is inside for safety reason).

An illegal CANNOT claim immunity from legal process.