You'll probably have an 'exit interview', during which you can suggest that you'd continue to do the current major projects for 75% of what they're paying you now - but you'd be working off-site, against a set of milestones (just like a real contractor).
Benefits to them : They'd save on paying you to slack off... and on the various National Insurance stuff too. It would be a win-win.
Benefits to you : You'd get the opportunity to say NO, which seems like it would be a novelty. Moreover, you'd have time to pitch your services to others to fill up the other 50% of your time. Don't sign a non-compete, unless you're getting paid to do so.
