Have a client who has a £2000 tax credits overpayment which is being appealed currently with the I.R. It's an odd case where there were 2 separately self employed people working together in a "business" which went sour, and the clients old business partner has declared client earnt a lot more than she did (possibly to reduce her own visible earnings, and put the onus on the client relating to tax).

Main problem is that the client was paid cash in hand (which raises other issues), only records are held by the ex partner, and hence thats the main source of declaration and information to the I.R. Client has no records, and no proof that the ex business partner hasn't made these records up. (No copies of records have been forthcoming as yet to look at).

Will the favour always go with the person holding the records in a case like this, as there is no real counter evidence (apart from word of mouth), any recommendations on angles to approach this one?

Thanks in advance.