"It's Phat, not fat" says fast-food chain McDonald's and new partner Sony Connect as they announce their co-branding marketing campaign this week.

As predicted, the two firms have announced a move which means customers of the US burger giant will be able to access one free song from Sony Connect for every promotional Big Mac meal they purchase.

The scheme launches in the US, Canada and Puerto Rico this month and in France, Germany and the UK in July, the BBC reports.

The BBC also reports recent US and UK government warnings about rising obesity levels linked to junk food.

The government here faces calls to ban junk food ads in the UK to help tackle the rising tide of obesity, as a September report from the Food Standards Agency said there is a link between advertising and children's diets.

Sony Connect uses Sony's own proprietary ATRAC format for its downloads, which only works with Sony devices.

Napster and others also made their debut in the UK this month, and uses Windows Media Audio. RealNetworks will launch its Rhapsody service this summer, and this uses Real's own proprietary format.

Apple, which intends launching its service early this summer, uses its own proprietary format (FairPlay) for its digital music service offering.