Union has accused contractor of spending more than £28,000 on checks

Skanska has promised to investigate its use of the construction blacklist and has pledged not to tolerate any form of blacklisting on its sites.

The news comes ahead of the trial of Ian Kerr, the man accused of heading up the Consulting Association, which operated the blacklist. The trial is scheduled to begin on 27 May.

Construction union Ucatt said it had seen documents showing that in 2008, Skanska spent more than £28,000 on blacklist checks with the Consulting Association, alongside an annual subscription of £3,000.

Ucatt said each check cost £2.20, meaning the firm made about 35 checks a day last year.

Alan Ritchie, general secretary of Ucatt, who was on the Consulting Association's blacklist, said: “The level of blacklisting that appears to have been undertaken by Skanska is staggering.”

Earlier this month Ritchie held a top-level meeting with senior Skanska senior executives. The Skanska executives reasserted that all blacklisting on their sites had ceased and that an internal investigation had been launched into identifying who had authorised the blacklisting.

Ian Kerr who ran the Consulting Association is due to go on trial next week May 27. If as expected he lodges a guilty plea he will be tried in a magistrates' court, where the maximum fine is just £5,000.