In this situation, in a built-up area, are you obliged to allow the bus driver to drive out of the bay onto the roadway?

Yes, in a built-up area, a driver is obliged to enable a bus driver to join the traffic when the bus driver signals with the left indicator their intention to leave the bus bay. To do this, you must reduce your speed and, if necessary, even stop your vehicle. This obligation arises from Art. 18 para. 1 of the Road Traffic Act.