Why can't political parties fund themselves from membership fees like unions?

With the current debate over party funding, dubious donations and "cash for access", it's worth asking why political parties can't fund themselves from membership fees and avoid all the accusations of being in the pay of wealthy business tycoons or union bosses.

Trade unions (and Voice is different to most in that it is independent and so is not a member of the TUC, is not affiliated to any political party and does not have a political fund so all its thoughts and actions are dedicated to its members) have to rely on membership subscriptions for most of the income, along with minor sources such as advertising or commercial revenue.

Other membership organisations, like the National Trust, also rely on membership income and also legacies the moral advantage of the latter being that the departed can't influence policy or gain "access" to politicians as living donors can!

Voice offers a range of services to members from their fees and a range of subscription rates to meet the needs of different types of member, including free student membership.

Perhaps the parties are spending too much on trying to win our votes after all, the media and online coverage they get is free and the main parties are entitled to party political broadcasts at major elections.

The non-concessionary membership fees for political parties seem low single figures in some cases even for those on high incomes.

So come on political parties clean up your act, levy more realistic fees for those who can afford it while offering concessions for those on low incomes, and get recruiting!