Appeals and tribunals

A client has had a VAT inspection followed by a Letter of Direction from HMRC withdrawing her use of the Flat Rate Scheme and requesting further information in order to back date the withdrawal. I have already appealed to HMRC about the decision, which has been turned down. I still disagree with the decision. Should I go ahead and supply the further information required before appealing to a tribunal (ie after HMRC have calculated the amount of VAT they want to claw back), or appeal firstly against the decision before any numbers are discussed.? Thanks.