Britannia is a charter airline. They don't sell seats but provide transport for the tour operators that charter Britannia. A small side of their activity uses a scheduled airline call sign but it is not how a charter operation is defined.
The low cost operators however, operate a schedule time table like BA does but are not on the Britannia's market. I guess JMC could be seen as a competitor but here, I feel that contracts are concluded at a different level possibly involving the airline but more likely, the group that owns it.