Balfour challenged the way the vote was conducted after 441 of the firm’s 1,650 workers were balloted.

Unite members voted 360 to 81 for a strike but the result is now void.

The union is vowing to re-ballot members along with workers at NG Bailey and Crown House as the row over reform of the JIB pay and conditions deal rumbles on.

Unite national officer, Bernard McAulay said: “BBES is aware that over 80 per cent of Unite members who returned their ballot papers, voted in favour of strike action.

“But rather than listen and return to the negotiating table, BBES have chosen to hide behind draconian ballot laws and challenge the democratic voice of BBES employees by quoting concerns, as to whether they have been advised of the correct name of workplaces and concerns, as to whether a handful of staff employees received ballot papers.”

A Balfour statement said the firm was “pleased that Unite has re-considered its position on strike action arising from the recent ballot, following a number of very significant deficiencies in the ballot identified by BBES and drawn to Unite’s attention prior to the announced result.

“We are keen to talk to Unite about moving forward with the BESNA, and for Unite to recognise the importance of implementing a new more modern agreement better designed to suit the needs of the industry and our customers.”