When Contract Compliance auditing first began we ran a successful line of defence against the deliberately slewed samples they selected. An early favourite were criminal Higher Standard Fees claims which, if assessed down to Lower Standard fees, delivered a hefty reduction and an almost certain category outcome and consequently some recoupment.
Exceptional claims contain a similar risk, though minus the extrapolation risk - you've just done 3 times the SF, lose some on assessment and get a maximum of a third of you profit costs. We costed our first exceptional Public Law level 3 case yesterday which had costs just above, some £200, the 2 times exceptional threshold. If this is reduced on taxation by about that much the firm in question stands to lose over 4 grand (once enhancements have been added in etc.)
They are fiddly to prepare as well apparently.
Be prepared to march into Court to challenge the provisional assessment. Interesting that as you are only £200 over the exceptional limit, your costs draftsman's fee was the factor taking your client over the limit (unless you are very very cheap).