For UK energy suppliers, times are tough. It is little surprise therefore that two of the big six – SSE and Npower – want out. But the merger of the two companies which hit the headlines this week has nevertheless created a stir. What’s the strategy behind the move? Is this the spark of a merger spree that will condense the big six into the “big three” and how will the tie-up affect the competitive dynamic of the much-maligned domestic energy market?