If IPs are required to do work outside of the usual scope, then it is right that they be paid for this work. So I agree with the basis of charging variation fees - sadly these days many creditors do not.
The meeting is necessary, in order to reduce this posters payments to ensure that the IVA continues to be viable, so there is no reason why the IP should not be paid for additional work carried out, and £500 seems more than reasonable. I suggest that you ask for this to be included as an additional cost of the arrangement rather than extra monies you have to find, though.
Regards, Melanie Giles, Insolvency Practitioner for over 20 years.
To have me propose an IVA for you, please visit:
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http://www.iva.com/iva_companies/IVA_Advice_Bureau.asp