It seems that part of their argument is based on survey data, and the rest is questionable:
They rely on data from a previous report that cited savings as follows:
i)Dismissal rates were lower in unionised workplaces with union reps – this resulted in savings related to recruitment costs of £107m-£213m pa
Surely this is because the Unions make it hard to fire people. So if someone is crap at their job, you can't replace them with someone good at the job. Without looking at the relative productivity rates of unionised vs non-unionised workplaces this is meaningless, but I reckon that preventing you from firing people who are crap would lower productivity and thus constitute a cost, rather than a benefit - and the magnitude of that cost will be significantly greater than the benefit, as you'd not want to sack someone unless you could get a better person in and make more money after costs were taken into consideration, so the costs must be smaller than the benefit.
ii) Voluntary exit rates were lower in unionised workplaces with union reps, which again resulted in savings related to recruitment costs of £72m-143m pa
People stayed longer (albeit because the benefits/pay were likely better) - this could be a valid benefit.
iii) Employment tribunal cases are lower in unionised workplaces with union reps resulting in savings to government of £22m-43m pa
See (i) - this is likely because tribunals were threatened in any number of cases, and the employer forced to back down. If you sack less people, less people will complain. I'd count this as a part of the cost of replacing crap people with good people, and would expect the benefit thus to far outweigh this cost.
iv) Workplace-related injuries were lower in unionised workplaces with union reps so resulting in savings to employers of £126m-371m pa
Really? What were the additional costs of complying with increased health and safety requirements placed there by the Union rep?
v) Workplace-related illnesses were lower in unionised workplaces with union reps so resulting in savings to employers of £45m-207m pa
What about non-workplace related illnesses? Is this just a case of the union rep saying "don't put it down as workplace related, or you could get in trouble"?
Taking points (i) and (iii) as negative (i.e. assuming that the productivity increase from replacing bad staff would be at least enough to cover the costs of replacing bad staff twice) and disregarding point (iv) as we have no idea of the actual costs involved in reaching this point gives a total saving from having union reps on the order of £40m (using average figures).
By the methodology in the report, 60% of this is public sector, so £24m. Uprating to now gives £28.7m - call it £30m if you like. So we get a benefit of £30m for an expenditure of £113m. Sounds like a good deal to me...
They question the £113m figure, suggesting that £80m is more reasonable - so we're getting back a massive 38% of what we spend. That's the kind of deal our government should be fully in support of!