There’s a helpful and insightful post here from a  former party staffer.

I’ll say only this. The very first time I met a party staffer was in a bitter debate, in my then ward, about whetehr the Militant Tendency should be expelled (about three years before the leadership were). A relatively senior party staffer also lived in the ward, and took part in what was, it’s fair to say, a lively debate that I lost. (I didn’t think our biggest problem in 1982 was whether we should expel Militant). After the meeting he didn’t threaten me with party discipline, or rail at me. We went for a pint and a long chat, during which he explained his point of view and laid out his evidence. And we parted as friends, with me persuaded that he was one of the good guys.

By the end of the Kinnock era my view of party staff was changing. Increasingly the top down drive to make the party more electable by making it seem less like a forum for dissent meant staff were becoming gatekeepers not enablers. The inevitable conclusion of the process was, as is pointed out in the post on activewiththeactivists, the substitution of party staff for the party membership in roles that the membership would previously have done.

And in the process we became a party dependent on donations to pay for the staff who were doing things that members used to do for nothing.