Agree with JT above, the arrogance of the "traditional" unions in thinking they had a remit to dictate national political policy is surely their main mistake. For non UK readers the traditional unions almost entirely funded the Labour party (and still do) and thus have an extraordinary power in dictating Labour policy which is especiallty unnerving as most of these unions were, and some still are unashamedly Marxist. This sort of dinosaur intellectuality brought their crazy ideology into disrepute even with many Labour voters, and their outrageous and pie-in-the-sky demands to perpetuate obsolete and damaging work practices and subsidies for dead-duck industries came to a head in 1982 with the suicidal miners strike. Mrs Thatcher had the guts to finally stand up to this tyrrany and broke lemings once and for all.
Trouble was, the remaining unions, even the responsible and non political, non militant ones like BALPA remain tarred with the same militant brush and are still regarded by many in "management" with suspicion as wreckers instead of an asset.
The overt politicalization of UK unions had dulled their credibility as workplace negotiators as much amongst the workers (ie us)as with the bosses and the media.
The lack of success with UK unions (ie BALPA) today in supporting the needs of its members is down to the disillusion of those members with the ability of the union to work...It is a self-crippling system, it is OUR fault. The law hasn't helped, but the legal system is nowhere near as restrictig to union activity as some would have us believe.
Our continental cousins have no such problem with standing up for themselves which is why the are are such horrific discrepancies between us as 40% pay differentials amonst members of the same company separated by a mere 150 miles - and crucially a bit of water. Differences like a workforce being offered destruction of their lifestyle or take substantial pay cuts in an almost ludicrously profitable company, one that simultaneously showers Millions on its directors in a way that would make the shades of even British Leyland Directors, or those of BSA and Triumph blanch...
And despite these iniquities we still can't get membership of the union to a sensible level.
Our continental cousins are willing to help themselves. We aren't. Make no mistake, that's where the power is lost.