Dixie.
Such a situation again is not clear. Many proposals state that the equity is to be released at a maximum 85% loan to value and mention a de minimis amount of £5,000. However they also state that if the IVA is not to be extended if '85% of your interest' in the property is less than £5,000. Therefore in your example there should be no extension as you cannot remortgage and 75% of your interest is less than £5k [assuming a jointly owned property].
However if the property is owned by you alone you would still be above 85% loan to value so a remortgage is out but 85% of 'your interest' is more than £5k so you could be caught with an extension. These are the sorts of problems that arise and need clarified with creditors and/or legal advice.