By Amber Murray The competition watchdog announced this morning that it had opened the first stages of an investigation into the tie-up between Carlsberg and rival drinks brand Britvic. Danish brewing giant Carlsberg agreed to acquire the British soft drinks maker for £3.3bn in July, in a significant push into the UK non-alcoholic drinks market. The CMA has opened invitations to comment on the merger in advance of any decision to launch a Phase 1 investigation formally. The CMA has issued a preliminary ‘invitation to comment’ to allow interested parties to submit their initial views on the tra…