The Collins review into the Labour Party's trade union link has two fundamental questions to consider.
The first is whether trade unions should continue the practice of collective affiliation, and if so on what terms.
The other is what role trade unions and their members should play within the Labour Party.
In an article in these columns last week I suggested that there were a number of options on which the principle of collective affiliation could rest.
But I suggested that the best option is the one currently operating, which is that it is up to each trade union to determine the basis of its own affiliation.
As explained last week, most of the affiliated unions now affiliate on a basis that bears some relationship to the number of members who pay the political levy.
But most unions under-affiliate. They do so out of respect for those members who do not support Labour and also to keep some cash for their own campaigns.
But what about the second question - the role that trade union members should play within the party?
Since the Clause IV debate in 1994, the rise of new Labour and the emergence of Progress the trade union voice has been gradually sidelined, and union leaders rightly feel that they are not being heard.
In my view the Collins review presents trade unions with the opportunity to reassert their role within the party.
A blueprint was prepared six years ago by an unofficial independent commission on Labour Party democracy convened by Labour Party activist Peter Kenyon, in which trade unions took part.
Indeed not only did unions take part but all of the existing "big five" at the time took part, each represented by very senior officials.
Other members of the commission were drawn from the Scottish Parliament and Welsh Assembly, and another is now an MP.
Chaired initially by Michael Meacher MP and subsequently by Angela Eagle MP, the commission proposed - among other things in a tight 58-page interim report - a 10-point charter of members' rights.
This would give Labour Party members rights of a wide and varied kind in relation to party organisation.
These include the right to select parliamentary and other candidates, participate in policy development, select the party's representatives for appointment to the House of Lords, have access to party financial information and to complain about unconstitutional or unethical behaviour to a party ombudsman.
One failing of the commission - of which I was a member - was that it neglected to spell out the role of political levy paying members of affiliated unions in these different processes.
The Collins review should fill that void, as a catalyst to democratise the party in a way that is progressive and inclusive.
So what role should unions want for their levy-paying members from the Collins review?
How about starting with, first, the right of access to party finances - to reflect the right they have to their union's finances - and second the right to take part in the selection of party candidates?
And how about third allowing union levy-paying members to vote with party members for House of Lords nominations and fourth giving levy-paying members the right to take part in a meaningful policy development process, by restoring the authority of conference and abolishing the ridiculous National Policy Forum?
While we are at it, post-Falkirk, who can now say that a party ombudsman is a bad idea?
Here was a recommendation that is becoming all the more compelling as the Falkirk drama unfolds, with Tom Watson's most recent revelations only the latest in a lamentable tale of party mismanagement, if not worse.
But for Collins the big issue is candidate selection, an issue now linked with the idea of "primaries."
Primaries are of two kinds - open whereby anyone on the electoral register can have a vote to select a Labour Party candidate and closed whereby only party members or supporters can have a vote.
Open primaries are used extensively for candidate selection in the United States but have no place here, except perhaps in safe seats.
As a general principle it would be nuts to allow the supporters of other parties to choose a Labour Party candidate, for reasons that ought not to need explanation.
Nor is there much to be said for closed primaries if by closed primaries it is meant that registered Labour Party supporters should be permitted to take part.
There would certainly be no justification for allowing such supporters to participate on equal terms with fully paid-up party members.
This is not to deny that the system of candidate selection needs to be opened up.
But the best way this could be done would be formally to enfranchise trade union members who pay the political levy in their union.
They should have a vote in the selection of the Labour candidate where they live.
The problem here of course is that the levy-paying member only pays £3 annually, while the individual member pays £44.50.
It would be hard to argue that both categories should have equal rights on this model, even though there are at least 10 times a many trade unionists affiliated as there are full members.
The answer is surely that on this model, there should be an electoral college in every constituency in which 50 per cent of the votes are assigned to party members and 50 per cent of the votes are assigned to trade union members resident in the constituency who pay the political levy.
Similarly with the House of Lords, until such time as it is abolished, replaced or reformed.
An electoral college could be created in which half the votes are assigned to party members and the other half to the political levy-paying trade union members, in what could be national or regional party constituencies.
But whatever happens it is essential that trade unions stay and fight.
If we go down the Miliband route of atomised associate membership of the party by individual trade unionists this will not only lead inexorably to an even further decline in union influence in the party but to their exclusion altogether.
The risk is that to appease and placate the leadership in the run-up to the election we give it what it wants.
Suppose Labour then wins the election. It is quite possible that one of the new government's early steps will be to "rearrange" the system of state funding for political parties.
What then for the Labour Party's trade union link?
But let's suppose that Labour does not win the next election. This is an outcome not as implausible as some may think.
How many trade unionists at that point will want to be "associate members" - or indeed any kind of member - of the Labour Party?
What then for the Labour Party?
Keith Ewing is professor of public law at King's College London.
For details of the Defend the Link meeting at Conway Hall, Red Lion Square, London on September 3 at 7pm, go to www.l-r-c.org.uk. For the Interim Report of the Independent Commission on Labour Party Democracy visit www.labourdemocraticnetwork.org