Finance Minister Lim Guan Eng is mistaken in his latest accusations on the Tax Refund Fund (TBBC) against the previous BN administration, claims his predecessor Najib Abdul Razak.

In a Facebook post today, the former prime minister said this is because Lim probably "did not understand" the correct accounting standard used, which is a "mistake anyone can make."

Najib said the finance minister had confused the modified cash accounting standard used by the government with the accruals accounting standard used by the private sector – leading him to draw the "wrong conclusion" that BN had misreported on taxes and falsifed accounts.

"It looks like our finance minister does not understand that the government uses the modified cash accounting standard, and not the accruals accounting standard, as practised by the private sector.

"Under government administration, for cash accounting, all financial transaction is calculated and recorded when there are cash deposits and withdrawals for the reported financial period," his post read.

Najib added that under the modified cash accounting standard, assets are not capitalised and liabilities are not reported in financial records.

With the accruals accounting method, revenue and expenses are instead recorded when they are incurred, and not when cash transactions are made.

"As with the 'confusion' over decimal points, the misunderstanding between cash accounting and accruals is a simple mistake anyone can make," he quipped, referring to the finance minister's admission of error in Dewan Rakyat more over two weeks ago.

Lim had stated that the shortfall in the trust account for GST refunds, RM19.248 billion, was actually higher than the RM17.911 billion previously disclosed, as a Finance Ministry staffer had made a decimal error during calculations.

Najib also said on Facebook that during his administration, the then-government was in the midst of transferring to the accrual accounting in the coming years as part of its efforts to transform the public sector.

His post comes after Lim accused former Treasury secretary-general Mohd Irwan Serigar Abdullah of not heeding the Inland Revenue Board's (IRB) request to transfer the necessary monies to the TBBC.

The finance minister stated that as of May 31, there was just RM1.486 billion left in the fund, claiming the previous administration had recorded money meant for refunds as revenue "to show a surplus."

Police are investigating the matter and have recorded a statement from Lim.