People who post one-off offensive messages on social media could escape charges under new guidelines, the most senior prosecutor in England and Wales has suggested.

"The time has come for an informed debate about the boundaries of free speech in an age of social media," Keir Starmer said.

One-off messages which do not form part of a campaign of harassment and are not intended to incite others are unlikely to lead to charges, the Director of Public Prosecutions signalled.

His comments came as he announced no charges would be brought against a Welsh Premier League footballer who posted a homophobic message about Olympic diver Tom Daley.

Daley, 18, and diving partner Pete Waterfield missed out on a medal at this summer's Olympics when they finished fourth in the 10m synchronised dive.

Port Talbot Town FC midfielder Daniel Thomas posted a homophobic message on Twitter, which was later distributed more widely, leading to his arrest, but Mr Starmer said the message was "not so grossly offensive that criminal charges need to be brought".

"It was not intended to reach Mr Daley or Mr Waterfield, it was not part of a campaign, it was not intended to incite others and Mr Thomas removed it reasonably swiftly and has expressed remorse."

New guidelines for prosecutors are needed because this was one of a growing number of cases and there are likely to be many more, he said.

Within hours, Greater Manchester Police announced the arrest of a 22-year-old man after a Facebook page was set up lauding suspected police double killer Dale Cregan as a "legend".

Mr Starmer said: "To ensure that CPS (Crown Prosecution Service) decision-making in these difficult cases is clear and consistent, I intend to issue guidelines on social media cases for prosecutors."