I have a copy of Airline Publication and Sales 'UK and Eire Commercial Airports' published in 1974. It refers to a seasonal service to Jersey operated by Dan Air from Swansea Fairwood Common using the 748 together with charter operations by Alidair (Viscount) and BIA (Herald).
Viscounts, both 700 and 800 series, flew in Dan Air colours in the early eighties. Not sure whether they were owned/operated by Dan Air or on some sort of lease agreement.
Jersey was, until perhaps the nineties, a very popular destination with multiple flights on Summer weekends as both schedule and IT charter services from all main airports, at least in England and Wales.
Swansea, along with other places like Coventry and Gloucester/Cheltenham that no longer have scheduled services at all had summer flights to Jersey. Going back to the fifties even Northampton Sywell had a (DC3) service to Jersey.