Nothing sells a scandal better than discovery. When a stone is lifted for the first time and something unpleasant crawls into the light, a nation draws up its skirts in horror. But to ask our fellow citizens to be shocked at something that has been going on openly for years is a taller order. Gordon Brown, however, may just have handed the Tories the means to do so.

David Abrahams's gifts to Labour are dwarfed by the trade unions'. About £10 million is being taken by stealth from union members every year, and given to a party that many of them do not support. They are not being informed of their right to opt out, nor even (in many cases) that they are contributing.

In the past six years for which I've seen figures, £85 million was collected by trade unions from their members and given to the party that governs Britain. In return the party gave these unions massive voting rights in its policy decisions and its leadership elections.

But approach the websites of Amicus, Bectu, BFAWU, Aslef, Aspect, Community, Connect, CWU, EIS, FBU, GMB, NASUWT, RMT, TGWU, Ucatt, Unity or Usdaw as a would-be applicant for membership, and in no case that I can establish does the online application form notify you of your right to opt out of the system of “affiliation” to the Labour Party. “Affiliating” on behalf of members allows the union's political fund to pay whopping “affiliation fees” (plus, often, cash donations too) to Labour.

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BACKGROUND

• A walking paradox who gave £600,000

• Brown is made to play the fool in stage farce

• Jack Dromey declares he is victim of concealment

Not that as a potential recruit to the union you are likely to be inquiring in the first place. Dig around elsewhere on trade union websites and you may be able to find that most do mention somewhere that joining the affiliation scheme is not obligatory. But is there a discount in that case? Eleven of the eighteen unions listed above make no mention of any possibility of a reduced membership fee, should an applicant opt out. So to most union members it does not appear that they could get their money back if they opt out. In which case why even bother to try? Few surely will.

Let us sum up. In the online form an applicant must complete to join, would-be members are not being notified — by the overwhelming majority of trade unions — of any right to opt out of political affiliation; and though elsewhere on most (not all) of their websites it is possible to discover that this right exists, the majority make no mention of a possible discount. Is it an unfair summary of the position to say that applicants with no particular wish to give money to the Labour Party are being being thrown off the scent?

It would certainly seem so. So successful has recruitment to their affiliation schemes proved that Usdaw and Nacods have managed to affiliate to Labour on behalf of a claimed 100 per cent of their members. CWU has done even better, with 104 per cent of members affiliated. Amicus is the winner, however, at 109 per cent. These are not secret corruptions, but openly accepted practice. The explanation for such Soviet results is that the Labour Party receives £4 for each trade union member affiliated. The money buys Labour Party voting rights based on the numbers affiliated. Thus, in policy and leadership votes within the Party, a terracotta army of nominal “affiliated members” is ranged behind each union, who, to gain extra influence, buy as many of these dummies as they can afford, at £4 each.

You will see at once that the connection between the individual union member and the Labour Party is a convenient fiction. However ancient, the situation is scandalous; but its antiquity has created difficulties for all the opposition parties in raising awareness and exciting the indignation that the circumstances merit. I've seen fellow commentators describing it as “an old chestnut” or “something the Tories have been going on about for about a hundred years”. How can opposition parties challenge these world-weary sighs?

Mr Brown has just provided the weapon they need. He has offered to involve all parties in putting the party funding debate back on to political centre-stage. In a panicky attempt to move the news focus away from the Abrahams scandal, the Prime Minister has offered to restart interparty talks on Sir Hayden Phillips's proposals for reforming party funding. Since these had foundered mainly because Labour would not move on the trade union question, Mr Brown will now have to agree to open that back up for discussion, or he will widely be seen as having acted in bad faith.

But for Labour this is a terrible debate to get into, not least because there's reason to think union practices may already be illegal under the Consumer Protection Act 1987, the Consumer Contracts Regulations 1999 and the Consumer Protection (Distance Selling) Regulations 2000; and, if not already illegal, may be outlawed by EU-inspired legislation coming into effect next year, according to which it will be an offence to induce anyone to enter a contract by “omit[ing] or [hiding] material information, or [providing] it in an unclear, unintelligible, ambiguous or untimely manner”.

As so often with Mr Brown, I believe, too much tactics has led to a strategic blunder, and this one (unlike the Abrahams affair, which was simply embarrassing, and would have passed) could put him at odds with his own party on something important to its heart as well as its wallet. I feel a twinge of sympathy for Labour traditionalists. It is difficult making the case in 2008 for what in the context of 1908 was perfectly logical, even noble. Labour used to be the political wing of the union movement and this justified the special link, without which many of its great purposes could never have been achieved.

But the case today for political parties that nobody affiliates to or contributes to, except intentionally, is very strong (as it is for modern trade unions whose core purpose is to advance their members' interests without fear or favour, with all parties equally, and with none). I don't see how it can be resisted. This would cripple Labour financially.

For their part the Conservatives, prepared already to concede a £50,000 limit on individual and corporate donations, have everything to gain from this battle — or, rather, less to lose. They will fight hard for the right to pump big money into marginal seats but, though useful, it is nothing like as important to them as is union funding for Labour. Nor are “communications allowances” (which make it easy for sitting MPs to spend state money on advertising government success) impossible for Tories to swallow. The entrenching of incumbency is a great evil, but one from which they too could benefit.

And if, in the end, a Labour government does go ahead (as Mr Brown has blustered) and legislate without all-party agreement, this gives the next Conservative government the green light to act in a similarly unilateral way, and smash completely the financial link between Labour and the unions. Gordon Brown may next year live to regret Phillips more than this weekend he regrets Abrahams.

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