If they don't take the fight to Parliament Flaperon, then they are not concentrating on their members interests.
And the more that can be achieved in Parliament, the less the need to take industrial action.
Every trade union should have a political fund so that it can engage in the democratic processes which provide the opportunities to secure improvements for it's members. And to defend existing gains.
Every great reform in the interests of ordinary working people during the 20th century, originated from the trade union movement – they all started off as a simple motion passed at a trade union branch meeting.
Having said that, obviously trade unions shouldn't waste their money by handing it over to self-serving New Labour careerist who couldn't give a toss about the trade unions or working people, and only care about their own fat arses.