The keyless entry and start don't work. The buttons on the doors or fob won't open the car. I can open and lock the vehicle using the keyblade, but this sometimes sets the alarm off. When starting the vehicle, I get a key not detected error unless I tap the key somewhere on the steering wheel column while pressing the button. While driving, I get the error key not detected, or sometimes the key is outside the car message.

I've changed both key fob batteries twice, but it didn't make any difference, so I'm thinking it must be the car, not the key I've also checked the fuses and charged the car battery, but no improvement. Is there anything else I should check before taking it to the garage?

We've seen a lot of rubbish new batteries lately.  Worth checking them with a multimeter to rule that out.

Next step is to check the remote receiver.  It's in the roof lining above your head.