She would not say if she had been asked by any of the main parties to stand as their candidate, adding she had been a floating voter all her life and would find it hard to follow a party whip.
Nigel Huddleston, who is due to fight the contest for the Conservatives, said only a vote for the Tories would "guarantee change" by ousting the government.
"That Ms Rantzen continues to be so interested in Luton - where she has no apparent links and even though Margaret Moran is standing down - has surprised many Lutonians," he added.
"If you're going to stand as an anti-sleaze candidate, surely it would make most sense to stand against an actual wrongdoer. They are hardly in short supply."
Prime Minister Gordon Brown has to call the next general election by next June.
At the 2005 general election Labour MP Ms Moran won with a majority of 5,650.
Following weeks of revelations in the Daily Telegraph about claims MPs had made on their second homes expenses, Ms Moran was effectively deselected by her party.
A Labour scrutiny panel ruled she, Elliot Morley, David Chaytor, Ian Gibson and Jim Devine could not stand for the party again.
Announcing she would step down she said she had "done nothing wrong or dishonest" and always followed advice from the Commons Fees Office.
But she said the "understandable anger" at the expenses claims had had "a bruising effect" on her and her family.
Since the expenses revelations were published more than 20 MPs have said they will stand down at the next election.
Ms Rantzen recently courted controversy on BBC One's Question Time when she made a remark about people in Northern Ireland being "addicted to hatred" - following a spate of attacks on Romanians in Belfast.
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