Horizontal integration & government regulation: Sainsbury's and Asda merger blocked!

Click on this link to read an excellent and timely piece on the proposed merger between Sainsbury's and Asda, two huger supermarkets in the UK.

There is so much Economics in this article. Points to discuss:

What is the view of the CMA?
What are the opposing arguments given by the Supermarkets involved?

Who is correct?

Is the market contestable?

What would the positives have been for the consumer if this merger went ahead?

What would the impact of the merger have been on efficiency?