Hi. You could pay off the IVA early -- but only from funds given or loaned to you from a third party (friend, family member, that sort of thing). If you came into any money ( inheritance, lottery win, big bonus)there is every chance that this money would have to be paid into the IVA anyway to increase the dividend to the creditors. This would not shorten the IVA unless you paid in your total original debt plus fees and, possibly, statutory interest.
If the IVA ends early you will be allowed to apply for credit -- but I doubt you would be given any as the IVA will stay on record until the 6th anniversary of it's start.
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014
The restriction on credit only applies where there is no consent from the IP. Many businesses continue to trade and obtain credit in doing so otherwise they would not be able to survive. It may be more difficult to source credit while in an IVA but it is perfectly acceptable to do so with the IPs approval.