This week, plumbers and electricians staged more protests in a dispute over pay and conditions. Protests were at sites in London, Cardiff, Manchester, Merseyside, Glasgow, Hull and North East Lincolnshire.

Contractors say changes proposed by seven construction companies would mean lower wages, but the firms claim many workers would benefit.

The union Unite said it had not officially backed the strike action. In a recent ballot union members had voted 80% in favour of strike action, which was originally intended for Wednesday, but Balfour Beatty Engineering Services challenged the walkout and a re-ballot was ordered by the trade union.

Blane Judd, chief executive of the Heating and Ventilating Contractors' Association (HVCA), which represents the seven companies, said: "The claims by protesters and the Unite trade union that the new proposed agreement will lead to massive pay cuts and workers heading for the sack are total fiction.