Yes. If you do not you are in breach of the mortgage terms this could potentially result in the lender terminating and forcing you onto less favourable terms. Non.disclosure could also cause you future borrowing issues. Sack the estate agent.
Other things you should have considered….
Insurance, will need to notify or change
Appliance and gas testing
Smoke alarms / other landlord obligations
Tax – the rent is taxable and while you get a deduction for interest capital repayments are NOT allowable so you could bring in lessthan the mortgage after tax depending on your circumstances.
Tax on subsequent sale – not sure of current reliefs but if the property ceases to be your main residence you could end up with a tax bill when you sell if you rent it long term.