Strike action never works
And Ignite should know that. But there's other strategies for the modern day that they (or more likely the TUC) could adopt. How about either a league table of all large employers based on how they pay, and how they treat their staff, their employee relations, and their conduct during any disputes? Obviously Fujitsu would be jostling with DXC for the title of Britain's Shittest Tech Employer (or would they?). And that would be helpful to prospective applicants, it'd make recruitment more difficult, as well as highlighting to these companies' customers that they are dealing with a disreputable outfit.
The TUC would need an insight and data team to correlate all this, and make sure that the labelling has good evidential backup (to avoid having their arse sued off), but that team could also evaluate data on management salaries, director payments, company profitability, so that they can differentiate between the companies who HAVE to cut costs, and those who simply want to gouge more profit by crapping on employees, and fling that into the mix.
If the worst employers had a label, widely reported in the press (who'd love this) of "Rubbish employer: Avoid applying to this company", that would help put a whole lot more pressure on management than strikes, for the simple reason that strikes lower the payroll costs at companies who clearly don't care about their service anyway. And the recruitment impact goes beyond the unionised staff - as a manager, would you want your career stained by working somewhere like DXC, if they had the BSTE accolade. The press would love it.