Luton will not want to turn away the 100 or so executive jets that come in every day.
LLAO cannot in fact "turn away" any operator that wishes to use LTN since the airport is - in common with most others - licensed as a 'public use' aerodrome which means that anyone can use it provided they comply with the Terms & Conditions of Use and associated bylaws.
Two such T&Cs are that all operators must have a handling agent and that they must obtain a runway slot from ACL. In practice, this means that if the Luton-based ground handling agents either cannot or will not handle the flight (perhaps for example, because of a lack of staff or because their facilities are likely to be fully committed already), then it can't operate through Luton.
One 'wildcard' is that Luton's South Apron is being re-vamped and the work starts progressively on 7th January with complete closure for two months from 14th January when Harrods relocates. This will in effect, remove five stands from use.
The other issue that's likely to have an effect is if Northolt picks up any significant number of Heathrow's and/or Gatwick's corporate flights because the routes out of Northolt directly conflict with most of Luton's and so frequently cause delays to Luton's departing flights.