Looking at the S17 start of season report from ACL, market share of the top 10 airlines at Luton by ATM across the 7 month period was:
Easyjet 44.1%
Wizzair 28.9%
Ryanair 8.9%
Monarch 4.9%
Blue Air 3.1%
Vueling 2.7%
Thomson 2.7%
DHL 1.5%
El Al 1.1%
Transavia 0.5% (now left the airport)
A combination of WIzz + Monarch would have been expected to control 33.8% of ATMs at the start of S17. Add Easyjet and we find 77.8% of summer ATMs are in the hands of just 2 airlines.
Note to pedants - yes the percentages don't quite match due to rounding differences