@Alexander Hanff
Reading too many reports of American court cases, then ;-)
There's a Group Litigation Order, but it is opt-in rather than opt-out as a US class action is - it does not automatically include all potential plaintiffs (nor provide the defendants with a once-and-for-all ruling), so you have a bigger recruiting job on your hands. It also leaves all the plaintiffs potentially liable (I suspect jointly and severally) to their own (contingency fees/no-cure-no-pay can't be used) and any defence costs if they lose the case, which could be nasty.
Mind you, I think (IANAL,) this isn't relevant to anything under the Data Protection Act, where it looks like a criminal offence is being committed rather than a civil tort anyway. So you want to get the DPP on the case...
This doesn't mean that I don't think that hanging's too good for them, though...