If you visit www.iva.com, as previously suggested, you can check the reputation of the firms on there by the reviews people have put on about them.
Alternatively, the professionals who post on here, Melanie Giles, David Mond, Andy Davie, Michael Peoples. They all come recommended by the posters on here. Phone them.
Sharing from experiences of dealing with debt
The greatness of a man is not in how much wealth he acquires, but in his integrity and his ability to affect those around him positively.
Bob Marley. http://kallis3.blogs.iva.co.uk
The benefit of them compared to other DMPs is that they are part of the thinkmoney group, and therefore have other products under their umbrella such as car insurance, house insurance, banking, IVAs, Bankruptcy support, they can easily transfer your case between DMP to IVA.
I used Greg Penn for my DMP and all my creditors except HSBC agreed to it