Since the last European directive on liberalisation came into law for flights within the EU there has been no legal distinction between scheduled, charter or any other airline services. Within the EU any EU registered airline can fly where they like at whatever frequency they like and charge what they like. The only regulatory controls are flight operations, safety and maintenance. Regulators are not permitted to licence airlines unless they have sufficient finances for their planned flights . This is largely based on consumer protection. Some flights are referred to as charter flights and this is because there is a contract in place under which a charterer (usually a tour company or broker) agrees to pay the airline a price to operate the flight or series of flights.
Trying to find any real distinction between so-called scheduled flights, so-called low cost flights and so-called charter flights is as pointless as trying to imject a skeleton with penicillin. Most consumers do not care what type of flight it may be, most do not even care which airline it is. Price is the number one issue.
Look at Thomson Fly. There is no distinction in their marketing about whether it is a Thomson Charter flight of a so-called Lo-Co flight.
Just by way of an example, look up any route which is operated by Monarch, BA, Easyjet and several so-called charter airlines. You will find that the prices on them all change regularly. I have just done an exercise for a couple of routes in Julj this year out of Gatwick. Easy Jet has the highest prices. BA is sometimes lower than the others.
Basically all those old labels are useless. They are just flights.
For flights to places outside the EU (other than Switzerland) it is all different. The old fashioned distinctions remain.