The sparks warned that the protest will be the first round in an “Autumn and Winter” of discontent as angry workers fight plans by major M&E contractors to pull-out of the JIB industry pay and conditions agreement.

Protesters handed-out campaign leaflets to Balfour site workers entering the Blackfriars job.

A ringleader with a megaphone was also calling on workers to leave the job at 8 o’clock to attend a mass meeting on the City streets.

One demonstrator told the Enquirer: “There is a lot of anger about the threat to our pay and plans to deskill the industry.

“Electricians won’t stand for it and this is the first demonstration and you can see by the turn out that people are angry.

“This will only get bigger and we will be protesting at major sites across the country until the employers change their minds.”

The big employers planning to pull out of the JIB are Bailey Building Services, Balfour Beatty Engineering Services, T. Clarke, Crown House Technologies, Gratte Brothers., MJN Colston, SES and SPIE Matthew Hall.

The electricians claim the move will “de-skill” the industry and see some sparks suffer pay cuts of up to 35%.

Balfour Beatty security staff were on hand to keep an eye on the situation this morning.

As workers arrived at the site many took leaflets and listened to the demonstrators but the Enquirer didn’t see anyone from the site join the protest.

One demonstrator said: “This is just the start and today is about laying down a marker saying we are not simply going to accept changes to our pay and conditions.

“This is a grass roots protest which will only get stronger as more people realise the threat to their livelihood.”

Bernard McAulay, Unite national officer, said: “We recognise that conditions in the sector have got tougher and Unite is prepared to negotiate ways of working that address the industry’s needs through our existing agreements and industry boards.

“However, the way these major employers have approached negotiations is highly provocative and our members have reacted with anger.

“These employers are trying to use the current economic climate to push through their long-held ambition of introducing semi-skilled operatives on much lower rates of pay.

“These companies are still highly profitable and in fact the majority have seen large increases in their profits over recent years. Unite will not stand-by and allow this cynical attack on worker’s terms and conditions to happen.”