Urban Infrastructure Minister Paul Fletcher (Image: AAP/Mick Tsikas)

Urban Infrastructure Minister Paul Fletcher says a Senate committee cannot obtain spreadsheets detailing the top 20 marginal seats -- the basis for the government’s funnelling of commuter car park funds towards Liberal electorates -- because they are confidential cabinet documents.

By raising a claim for public interest immunity, Fletcher has ensured the documents will not be publicly available until at least 2039. Releasing them would have a “chilling effect” on the ability for comprehensive and candid discussions between ministers to take place in cabinet, he said in his letter to the committee.

Fletcher’s claim is the latest attempt by the government to avoid scrutiny over its administration of the $660 million commuter car park fund, in which 87% of the funds go to Coalition-held or targeted seats. And it’s one crossbench senators and transparency experts say holds little water.