Police say some of the online messages sent to the family were "extremely distasteful", but none would lead to prosecutions. 

[Gerry McCann said last year that trolls should be prosecuted]

No further action will be taken against dozens of people accused of targeting online abuse at the family of Madeleine McCann, Sky sources have revealed. 

Anti-abuse campaigners had compiled a dossier of names after becoming alarmed at the threatening nature of some tweets, posts and messages on online forums directed at Kate and Gerry McCann. 

Hundreds of messages have been posted by trolls who believe, despite no evidence, that the McCanns had some involvement in the disappearance of their daughter in Portugal in 2007.

In a letter to the campaigners, Leicestershire Police Assistant Chief Constable Roger Bannister said: "While finding that much of the material was extremely distasteful and unpleasant in nature, it was determined that none of the messages/postings constituted a prosecutable offence." 

[Madeleine went missing in Portugal in 2007]

Sky News Crime Correspondent Martin Brunt said: "Leicestershire Police had spent about eight months investigating the dossier, which effectively was a catalogue of abuse tweeted and posted online elsewhere by antagonists of Kate and Gerry McCann.

"There were dozens of such individuals identified in the dossier. They had threatened violence and even death against the couple."

The online posts included words like petrol and matches, handcuffs, shooting, torture and lynching, Brunt said.

One woman named in the dossier, Brenda Leyland, committed suicide after being confronted by Sky News.

Brunt said those who compiled the dossier have reacted with "absolute dismay" at the decision not to prosecute.

"They say it is tantamount to giving the trolls, as they call them, carte blanche to carry on abusing the McCanns," he said. 

[Stella Creasy (L) and Caroline Criado-Perez both faced online abuse]

"Although we haven't heard directly from the McCanns, I'm sure they too will be astonished because when Sky News revealed this dossier in September last year, Gerry McCann said such trolls should be prosecuted."

Successful prosecutions have been brought against online trolls in the UK.

In September, Peter Nunn, who sent abusive Twitter messages to Labour MP Stella Creasy, was jailed for 18 weeks.

The abuse started after Ms Creasy supported a successful campaign to put the image of Jane Austen on the £10 note.

Two other people who sent abusive tweets to Ms Creasy, as well as to fellow banknote campaigner Caroline Criado-Perez, were also given jail sentences last year.

Isabella Sorley was jailed for 12 weeks and John Nimmo for eight. They were ordered to pay £400 compensation to both victims.

In June, Jake Newsome, who wrote an offensive Facebook post about Ann Maguire, a teacher stabbed to death in her classroom, was jailed for six weeks.

Earlier this week, the McCanns won a libel case against a former detective in Portugal.

In his bestselling book, Goncalo Amaral claimed the McCanns hid their daughter's body and faked an abduction after she died in an accident.

A civil court in Lisbon ordered Mr Amaral to pay €606,000 (£433,000) to the McCanns