How do I disable VAT on some Write Offs but not others

Hi,

VAT accounting lines are generated when I write off an amount in a maintenance worksheet and arupdate, but these amounts are as a result of Bank charges which are not Vatable transactons. How do I turn off the generation of the VAT accounting lines specifically when I write off these amounts, but still retain the generation of  VAT accounting lines when writing off other amounts, i.e. not related to Bank Charges?

Rgd.,

CG