Northern Rock generally operate under a 45p in the £ criteria - that said I have seen a case go through recently based upon 40p so he might be lucky.
You should not offer your surplus income up to his IVA - but maybe keep that up your sleeve if he gets a rejection, so that you can help him to improve his offer.
With regard to credit rating, it will remain on his credit file for 6 years from commencement and not completion.
MBNA - very unhelpful at the moment. Make sure that he has taken steps to talk to them directly about his difficulties before he commences an IVA, and offer them some form of ongoing repayment plan (which they are unlikely to accept). Tell him to record the name of the person he speaks to and the date of the conversation.
Egg, Marbles, Halifax - are generally OK, but Egg do not like accepting IVA's where payments have continued to be made to them up to the date of the creditors meeting.
Regards, Melanie Giles, Insolvency Practitioner for over 20 years.
For further details contact me at
http://www.melaniegiles.com and view my IVA blog at:
http://melaniegiles.blogs.iva.co.uk