This is from the CAA website.
What situations does ATOL cover?
ATOL protection applies to virtually any overseas air holiday booked with a UK travel company. The law says your holiday must be protected if you book a holiday with a single travel firm that includes:
flights and accommodation (including a cruise), or
flights and car hire, or
flights, accommodation and car hire.
The scheme also applies when:
You book flights (including UK domestic flights) but do not receive your tickets immediately. This is most common with charter flights, but can also apply to discounted scheduled flights. Please note that ATOL does not apply to holidays or flights booked direct with scheduled airlines.
Your holiday involves at least one flight to or from the UK. For instance, a fly/cruise break where you travel out by ship and fly home, or a holiday in France where you travel out by Eurostar but fly home.
You book a package that includes UK domestic flights
So, are Monarch 'flight only' bookings, made via their website, ATOL protected or not?