Angela Rayner has been urged to come clean on the tax probe which freed up her path to No10.
HMRC shut its investigation yesterday after the former Deputy Prime Minister finally paid her £40,000 tax bill.
Ms Rayner was found to have owed the hefty sum last year after purchasing a £800,000 holiday home on the south coast - and then failing to pay stamp duty.
But the process to clear her name was accelerated after her lawyers intervened and asked if her case could be wrapped up "as soon as possible" following Labour's disastrous set of local election results.
Following the so-called "sweetheart deal", Ms Rayner announced her name had been cleared by the taxman, potentially freeing up the Ashton-under-Lyne MP's route to Downing Street.
Nevertheless, the issue surrounding Ms Rayner's tax affairs is yet to be forgotten as she now faces calls to publish all correspondence with HMRC "in full".
Alex Burghart, Shadow Chancellor of the Duchy of Lancaster, said: "Angela Rayner's carefully worded statement cannot disguise the fact that she has still had to cough up £40,000 in a sweetheart deal with HMRC.
"It cannot be right that one of the top contenders to be the next Prime Minister only settles her tax bill for political expediency. If Angela Rayner cannot keep her own affairs in order, how on earth can she run the country?
Angela Rayner announced she had been cleared by HMRC yesterday
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"If she wants the top job, she should publish all correspondence with HMRC in full."
On Thursday, Ms Rayner's spokesman said HMRC's probe found that the MP acted with "reasonable care".
"HMRC concluded that she had not acted with any impropriety or carelessness and that accordingly no penalty is chargeable," he added.
Tax expert and founder of Tax Policy Associates Dan Neidle said he did not understand why HMRC had absolved the former Deputy Prime Minister after the PM's ethics adviser had ruled that Ms Rayner was "careless".
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Alex Burghart called on Angela Rayner to publish full correspondence with HMRC
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"The facts, as reported by the Prime Minister’s ethics adviser, were that she [Rayner] obtained advice from two sets of lawyers [on the purchase],” he told Times Radio.
"Both of them suggested she sought tax advice and she didn’t take tax advice at the time. That’s why the mistake was made.
"I said at the time, I thought that was careless. Her statement says HMRC have concluded [it] isn’t careless and are not charging a penalty. And I can’t explain why that is."
HMRC's clearance of Ms Rayner has built her path back to frontbench politics in Westminster after she resigned over the tax scandal last September.
The MP has become increasingly outspoken against her boss, goading on Sir Keir to welcome Greater Manchester Mayor Andy Burnham back to Labour's Westminster ranks.
Such support has contributed to mounting speculation Ms Rayner could form a "soft-left" coalition with the Mayor - although she has denied rumours of a Blair-Brown Granita pact.
The "King of the North" is eyeing up his second bid to return to Westminster after Labour's ruling body denied him the chance to stand in February's Gorton & Denton by-election.
Yesterday, Josh Simons, the Labour MP for Makerfield, said he would step aside and allow Mr Burnham to run in his place.