Labor MP Nick Champion has defended a letter sent to constituents which claimed he’d secured Holden’s Elizabeth production line until 2022 – but has admitted the statement could have been more detailed.

Champion sent a letter – obtained by the ABC and The Australian – to his Wakefield electorate claiming he had “secured guaranteed support for GM Holden, Elizabeth, ensuring production until 2022”.

Holden has said it will wait until after the federal election – and after workers vote next Tuesday on a new wage agreement – before deciding whether to invest $1 billion in Australia to keep the plant open.

This morning Champion told the ABC he was certain Holden would stay in Elizabeth, but admitted his letter did overly simplify the issue.

“It’s fair that you might make that criticism. But the way I’d respond is to say that three weeks earlier I sent a pamphlet out to the entire electorate which went into more detail but said basically the same thing, using basically the same language.”

Champion said Holden hadn’t personally guaranteed to him they’d stay in Elizabeth till 2022. However, he claimed the only uncertainty in that decision rested on the Federal Opposition’s plan to cut industry assistance if it wins government.

“They haven’t told me that personally, obviously. But what I am guaranteeing is that I have secured support.

“Basically we have put $275 million on the table in co-investment.

“They’ve said they might come back to government and have another discussion about that package. But what’s clear is that in Labor’s car plan, there’s capacity to do that.

“The investment in two new models, it’s contingent on co-investment. We’ve said we’ll put in $275 million, the Liberal Party have said they’re going to cut $500 million.”

The Opposition was quick to criticise the claim as misleading and untruthful.

“The lies don’t get much bigger, bolder or brasher than this one,” Liberal senator for South Australia Simon Birmingham told the ABC this morning.

“There is no commitment under any political party from Holden to guarantee production until 2022. There’s a choice that Holden faces, and there’s a choice that the electorate faces, and that choice is the Liberal Party is offering a lower-cost production environment.”

Birmingham said an Abbott government would cut business red tape, end the price on carbon, and undo the changes proposed by the Rudd Government to the fringe benefits tax – all of which would improve the outlook for the Elizabeth plant.