Originally Posted by
Expressflight
I thought that as well. I remember it was part of the restrictions announced to keep LTN within its overall noise limits that no daytime diversions other than emergencies would be accepted between June and September 2018. Maybe those restrictions have since been amended unnoticed.
They are indeed banned.
Signature Flight Support | London Luton Airport Night Noise Closures
Also appears as a PDF from the airport direct.
Maybe they were four emergencies