It's almost a year since the supermarkets went to war with the brands on their very shelves, with TV ads and new web features provocatively urging consumers not to buy bestsellers such as Warburtons bread and Pepsi cola, but to choose own-label alternatives instead.

Sainsbury's Justin King went so far as to describe the battle as "Darwinian". And when I quizzed him on the merits of slagging off brand owners who were spending billions to create and build new products and new categories, supporting trade investment demands and complying with onerous supply-chain instructions, he brushed it off as healthy competition.

Judging by the news this week that Diageo is suing Sainsbury's over copyright infringement on its Pimm's drink (see p4), it would seem the drinks manufacturer doesn't see the current competition terms in quite the same healthy way. While Sainsbury's crowed in its internal newsletter that its Pimm's alternative, Pitcher (£10.79 for 70cl), actually tasted better than the original (£12.56 for 70cl), Diageo appeared to be mischievously striking back, promoting a whole litre of Pimm's in Tesco and Asda over the summer for £9.99.

Now, buoyed by positive noises emanating from the European Court of Justice in a copyright infringement case brought by L'Oréal, Diageo believes it's time for prosecution.

It has been widely assumed that suppliers were reluctant to challenge the supermarkets over copyright on the grounds they were too important. Prosecution o'clock suggests Diageo was merely waiting for a change in the prevailing legal wind and will be closely followed by other brand owners.

But one must wonder whether own-label gains and the increasingly provocative rules by which supermarkets play also had a part in Diageo's decision. After all, you can be sure if a retailer set itself up with an orange livery under the fascia name Sainsberry's, the Holborn lawyers would be on them in a flash.