I would suggest that you take into account the remaining number of payments - ie 43 @ £280, plus the value of your equity in the property now, based upon the 85% LTV rule.
You will also need to demonstrate to creditors the reasons for wanting to settle early - ie are you struggling with the payments, as they may wish to take their chances on the property market increasing in value.
I would not accept your current offer if I were a creditor, but again be advised by your own IP who will have to account to you in the event of failure. You chose that firm to represent you because you felt they would do a good job, so have faith in them and be guided by them.
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