Hi Nick1 and welcome to the forum
This is something that really ought to have been thought about before your IVA ws put forward. I always look at the possibility of this occuring with my own clients, and if there is a risk that a vehicle may not last for the five years an IVA will run over, then it is probably better to seek finance prior to entering into the IVA. This is always then disclosed within the IVA proposal.
You will need to discuss with your IP the implications of buying a replacement car on finance, and the effect this will have on your contributions. If there is a need for a reduction, then this can only be done with the express resolutiom of your creditors at a newly convened creditors meeting, and they are never keen to see variations during the first year to be frank.
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