A far as i am aware yes you do need to declare it, if you have inherited enough to pay the iva off then why not offer it as a full and final payment. You need to speak to your IP about it and they will tell you the best options open to you.
If you are already on an IVA then yes it will certainly need to be disclosed. If you are thinking of one, and feel that an inheritance may be likely, then perhaps you will need to factor that into your decision.
Best to get some professional and impartial advice if that is the case, and speak to as many organisations as you like, all should be happy to give no obligation advice if needed.
Regards.
Cert DR
23+ years in debt advice
I do not post for anyone other than myself