the problem surfaced again in the late 90's iirc about UK tour operators and seat brokers chartering eastern european airlines at that time for seasonal work due to the decline of small or niche UK charter airlines -
we had lost AE CKT BIA FCA IEA Airways Intl Cymru Amber Air Ambassadair Leisure Intl BWA and DA all in the 90's and we were left with just the biggies BY AIH and JMC and family owned MON...
no small ones at all - and now we have none really as MON is gone.
the EU stepped in as iirc they tried to use JAT and possibly aviogenex after the Yugo war as they had spare a/c sitting around
and I think viking and/or goldcrest brought them into the UK one summer and the CAA and the EU banned them - I seem to think that is when transwede got a toe hold into ops out of LGW
now all the niche airlines operating in the UK are pretty much now EU or eastern european or turkish such as Germania ASL Volotea Albastar Small Planet Freebird smartlynx etc - we have no niche carriers left except maybe Titan and Flybe who have the odd own IT charters for corsica menorca skiathos or skiing
ironically BA now for past few years operate a large IT charter program at weekends from LHR and BACF with the EMB fleet from the provincials in england IOM and Scotland