The insurance policy says the car should not be left with keys in, on or in the immediate vicinity of the vehicle. I would say inside the house, and not in immediate view from outside, is not in immediate vicinity,
For the garage provision in the T&C's, it appears very strict although the question when closing the policy was more around "do you have a garage" rather than mandatory use. (none of my neighbours use theirs). Would need to look up details online again. Give me 5 minutes.
Loss or damage caused by failure to protect the insured car, (see ‘Care of
the Car’ under the general conditions), or if it has been left unlocked and/
or with the keys, lock transmitter, entry card or other ignition control device
left in, on or in the immediate proximity of the vehicle.
For garage, policy says "overnight location" : Garage. Policy has general security provisions/advise around putting car in the garage overnight, but explicitly states that this does not form part of the policy.
Does this help?