Blacklisting campaigners called on MPs to stand up and be counted yesterday after revelations surrounding police spying on builders added fresh fuel to the demand for a full public inquiry into the sickening victimisation of workers.

The Met’s notorious special demonstration squad (SDS), whose officers also infiltrated environmental groups, sent officer Mark Jenner to join construction union Ucatt.

Posing as a joiner called Mark Cassidy, Mr Jenner was a Ucatt member from 1996 to 1999 and took leadership roles in a number of organisations associated with the union.

The union’s general secretary Steve Murphy branded the discovery “a scandal that must be exposed.”

In his time undercover Mr Jenner embarked on a five-year relationship with a female activist involved in related campaigns.

She told the Daily Mirror: “It is appalling they spied on people who were arguing for better health and safety at work.”

Mr Jenner also operated within the Colin Roach Centre in east London, a centre of activity for campaigners against police brutality.

His diary, which he left in his ex-partner’s possession, shows that a substantial amount of his time was taken up with union activity.

A database blacklisting thousands of construction workers — including many working during the same period — was seized from the Consulting Association in 2009.

Some of the entries included information that could only have been supplied by the police or security services, a senior official at the Information Commissioner’s Office, which seized the database, has said.

In a statement the Blacklisting Support Group said: “Blacklisting is no longer an industrial relations issue. It is a national scandal — a conspiracy between big business and the police to spy on union members.

“The Blacklist Support Group challenges every politician standing in the general election to answer one question: do you support a fully independent public inquiry into the blacklisting scandal?”

Anti-police-surveillance campaign group Netpol said the revelations “show just how far the SDS was spreading its wings.”

And Netpol spokesman Kevin Blowe told the Star: “The covert surveillance of protesters still continues to this day, largely unregulated and unchecked either by courts or by the police themselves.

“There’s still ambivalence from the police as to whether they still see (engaging in) relationships as acceptable practice.

“A different type of trade unionists are under surveillance, but they’re still seen as a threat for exercising rights either to go about their job, or make sure their job done safely.”

Mr Murphy said police chiefs “operated a secret organisation that destroyed innocent people’s lives.”

He added: “This sort of operation could only have been sanctioned at the highest level. Who gave authority for the police to do this and how high did it go?”