Yes, Smartwings do (did) fly for UK holiday companies,
One of the 737-800's flew IT weekly charters from Jersey to Tenerife and Malaga iirc (these were booked for a MAX from April but of course that's not possible right now)
They also used to do a lot to Greece and Greek islands for Olympic Holidays from UK but I gather that is all finished now also.
Update - for next season 2020 - No more Smartwings
For our 2020 Tenerife programme we are pleased to work with Spanish airline Volotea for Sunday day time departures. You will enjoy a quick and comfortable flying experience aboard Volotea’s new Airbus A319 jet aircraft. The modern jet will take you from Jersey to Tenerife South Airport in approximately four hours direct to the winter sun.
Palma and Malaga will be operated by Air Europa.