MOUFFLON more or less sums it up. In the UK, despatchers are not licensed individuals, whereas elsewhere, they are. It depends really on what you want from the job. If you want to bash out loadsheets all day long, then stick with the handling agents. If you want to go far deeper, suggest you contact the foreign airlines such as Saudia, AA, Emirates etc as they will obviously provide a far better training package than the likes of Servisair etc. The benefits will be greater too.
Now I wait for the slanging from Servisair bods
