EEC high flier stealing my French and German cash once (6,6)

'eec' is the definition.
(European Economic Community)

'high flier stealing my french and german cash once' is the wordplay.
'high flier' becomes 'comet' (object which flies through space).
'stealing' means one lot of letters goes inside another.
'my french' becomes 'mon' ('my' in French).
'and' is a charade indicator (letters next to each other).
'german cash once' becomes 'mark' (former currency of Germany).
'mon'+'mark'='monmark'
'comet' going around 'monmark' is 'COMMON MARKET'.