I agree with Anne, I don't think there are any requirements, certainly not for your own home. Rental properties may be different. I'm sure Paul will be along shortly. He'll know.
But if I had a gas boiler inside the main living part of the house, I would have a detector. I have always had the boiler in a utility room so haven't bothered with a detector.
With either scenario, it is a good idea to have an annual inspection. Peace of mind and all that.