Finance Minister Lim Guan Eng should lodge a police report over his allegation on the "theft" of goods and services tax (GST) refunds instead of hiding behind parliamentary immunity, said Najib Abdul Razak.

In a lengthy statement posted on his Facebook page, the former prime minister also claimed that the government stands to lose about RM31 billion, this year alone, due to the abolition of the GST in June.

This due to the three-month tax-free period before the sales and services tax (SST) is implemented in September.

"I want to state clearly that due to the tax exemption for three months, the loss of revenue is at least RM15 billion. There is also an additional RM8 billion loss for the months of September and December this year.

"By prematurely stopping the GST, the new government can be exposed to RM8 billion worth of input tax claims for the month of April and May where the government must pay it to traders who have the right to claim back the tax," Najib wrote.

This amounted to RM31 billion for this year alone and the amount could even go higher, the former finance minister added.

This because consumers would have purchased luxury goods like cars and other expensive things during the tax-free period, before the implementation of the SST, he pointed out.

"Besides, the abolition of GST and its enforcement system also provides room for tax dodgers and lower corporate tax declaration as what happened under the previous SST system.

"These are the real reasons why many promises in Harapan's manifesto cannot be fulfilled and why aid to the lower-income group will be further slashed and the pay raise for civil servants will be frozen."

Najib, who is also Pekan MP, dared Lim to personally lodge a police report on his claim that the previous BN government was involved in a "theft" of RM19 billion in GST refunds.

"Instead of alleging it in Parliament where they (Harapan) have immunity, Guan Eng should personally lodge a police report and state clearly how BN had robbed the billions.

"The rakyat now has to brace for various new taxes from Harapan due to the abolition of GST," he said.