I don't think you understand what I'm trying to do. The filtering of the items (forms) can be done when forms are submitted, but you cannot have permissions on views.
I want a Workflow to organise the forms into folders - each folder has specific user groups assigned to them so they could only see their own folder not anyone elses.
However, I took another approach and did not use Workflow at all.
I use the OnSubmitRequest method and some scripting to allocate the forms into the right folders. Works okay... but ideally, Workflows would be much better.