I have used telecanvasserrs and door canvassers.All self employed -as long as you dont dictate thier working hours and they use thier own transport,telephone etc they are legitimately freelance and therefore self employed.
Telesales canvassers are paid £4 per hour,£1.50 for every lead and 20% of job value..Data can be expensive but it picks up good work and helps to find nice little pockets which can then be further developed with door canvassing.
Door canvassers paid 75%-100% of job value.
This has worked very well for me.I have got a good little system in place
Check out my website under resources and you will find some useful canvassing information
Hope this helps :)Good luck with it..it will defo boost your business