By Amardeep Bassey / Birmingham Mail

An undercover cop who spied on eco-warriors by posing as one of them for eight years invited hundreds of fellow protesters to a three-day bender to celebrate his 40th birthday on a Midland farm.

Mark Kennedy had become so well “embedded” with dozens of protest groups that more than 200 people ranging from anarchists to animal rights activists turned up to his party in Herefordshire.

All of them were oblivious to the fact that he was feeding back detailed reports about them to an elite and secret Metropolitan Police unit called the Special Demonstration Squad (or SDS for short).

The secret unit was otherwise known as “The Hairies” because of its track record of infiltrating protest groups.

But just two months after the birthday bash the subterfuge ended for the man protesters knew as Mark Stone – or by his nickname Flash, earned because of his access to a seemingly never-ending supply of money.

Little did they know that their scruffy friend was on a £50,000-a-year basic salary, and had been handed a £200,000 expenses account to keep up his pretence of having been “involved” in the drugs trade.

It was in September 2009 that Kennedy was shocked to receive a curt text message from his police handlers, telling him that he was being “extracted” and that his alias Mark Stone would be summarily “dismantled”.

According to Kennedy, the message dryly added: “At least you had a great party – but now it’s over”.

Less than a year later, the father-of-three’s double life was uncovered by protesters who unearthed his real passport after becoming suspicious of the well-heeled warrior’s time spent among them.

A media storm ensued as Kennedy and fellow undercover officers were publicly outed amid lurid revelations that they stole the identities of dead babies, had illicit relationships with their targets and actively organised demonstrations, one of which later led to a collapsed trial.

Twelve women are currently suing the Metropolitan Police for emotional trauma, claiming they believed they were having a relationship with a fellow activist when, in fact, it was an undercover cop leading them on.

In separate proceedings Kennedy, now abroad in hiding, is suing his former bosses, saying police chiefs failed to stop him from falling in love.

Two inquiries by the Met and Her Majesty’s Inspectorate of Constabularies have reported serious failings in the now-disbanded SDS and its parent undercover unit, the National Public Order Policing Unit.

Over almost five decades, police spies have broken the law, stolen dead children’s identities, seduced their targets, fathered secret children before vanishing from their new families’ lives, acted as agents provocateurs, and attempted to smear and undermine critics of the police.

There have so far been 15 police inquiries in total, a television documentary, anguished exchanges in the House of Commons, the condemnation of police behaviour by the Prime Minister, and the promise of action from the Home Secretary.

The most recent allegations claim the unit was involved in a systematic spying and smear campaign against the family of murdered black teenager Stephen Lawrence.

Now, a new book by the two journalists who first exposed Kennedy and the SDS has revealed astonishing details about the “dark underbelly” of undercover policing in Britain, and more details of Kennedy’s sinister role.

Gleaned from the testimony of duped protesters and secret police records, the book – titled Undercover – paints a picture of a renegade cop who began to believe his own legend.

With easy access to cash and a growing penchant for drink and drugs, the book describes how Kennedy invited hundreds of protesters from across Europe to the 40th birthday party in the Midland countryside.

The extravaganza was advertised weeks in advance on flyers featuring pictures of John Lennon and Yoko Ono, and the iconic image of a hippy confronting gun-wielding police with a flower. Kennedy had even promised fellow protesters that he was flying a pop group over from Croatia to perform at the party.

“Eastern European anarchist punks” is how one betrayed activist recalls how Kennedy described the fictitious group that failed to show at his unsanctioned event in a Herefordshire farmer’s field.

Revellers were expecting a band like Pussy Riot, the Russian feminist punk band who were convicted of hooliganism motivated by religious hatred last year, and sentenced to two years imprisonment.

In the end, the three-day party went ahead with Kennedy performing with an impromptu rock band he had formed called “The 69ers” composed of fellow protesters born in the year 1969.