After you make the lump sum paymant the usual closure procedures will start. Depending on who you are with it can take between a couple of weeks to 6 months to produce your completion certificate --- until this is issued you are still in the IVA, although not making payments. Three months after the certificate is issued you will come off the Insolvency Register. Your IVA and defaulkts will remain on the credit files until the 6th anniversary of the start of the IVA, regardless of early closure.
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014 http://foggy.blogs.iva.co.uk
As Foggy says your credit record will show all the adverse information for the full 6 years so it will still have an impact. Where Mortgages are concerned for instance there are some specialist Lenders who may look to lend before the full 6 years is up but you would require a large deposit, minimum 25 - 30%.
IVA Mortgage Expert
Zebra Money Centre