I used to get good a good response from yell.com ads, but since around January this years they started putting sponsor ads at the top.
I've had several Priority web link adds, that put you at the top with others who have the same in your area, usually around 2 to 5 companies, so it worked well, BUT these sponsored ads now go ABOVE those, so there's always another 3 or 4 above the priority ads, and it's killed the response rate dead for both my Priority ads for 2 different services (£50 or so each per month)
I won't be renewing. You're better off spending the money on SEO work for your website IMO or other advertising.