Vince Cable may now claim that the Lib Dems only warned of the dangers of a VAT rise during the election in order to "score points" over the Conservatives, but there are others in his party who have always opposed this regressive move on principle.
One of them, Andrew George, has now tabled an amendment demanding an assessment of the impact the new 20 per cent rate will have on low-income groups. It has been signed by three others -- Bob Russell, Mark Williams and Roger Williams.
There is no evidence that Simon Hughes and Charles Kennedy have joined the rebellion, though it wouldn't be surprising if the Gang of Four (as they will undoubtedly soon be known) had their tacit support.
Meanwhile, Russell, who has previously threatened to vote against the Budget in its entirety, has dismissed an Independent on Sunday report that the rebels have secretly agreed to co-operate with Labour MPs as "poppycock" and "Labour mischief-making".
He said: "There is not a conspiracy involving Simon Hughes or Charles Kennedy, this is about backbencher unease from members. If Labour think there is some yawning chasm they are going to be sorely disillusioned."
It remains to be seen whether the amendment will be put to a vote on Tuesday, but the rebellion is an important reflection of the wider unease felt by Lib Dem activists over the Budget.
The MPs have no obvious ideological agenda, but Russell has a record as a Lib Dem maverick. He previously rebelled against the party whip to vote against equalising the age of consent and the sexual equality act.
Russell's name and those of his fellow conspirators are certainly worth noting for the future.
Constituency: St Ives (elected 1997)
Majority: 1,719 (3.7 per cent)
Significant moments: One of the first Lib Dem frontbenchers to threaten to resign if Charles Kennedy did not stand down as leader. Later sacked by Kennedy's successor, Menzies Campbell.
Constituency: Colchester (elected 1997)
Majority: 6,982 (15.1 per cent)
Significant moments: Rebelled against the party whip to vote against equalising the age of consent and against the sexual equality act.
Constituency: Ceredigion (elected 2005)
Majority: 8,324 (21.8 per cent)
Significant moments: Dramatically increased his majority at the last election from 219 to 8,324.
Constituency: Brecon and Radnorshire (elected 2001)
Majority: 3,905 (10.2 per cent)
Significant moments: Served as shadow Welsh secretary for the Lib Dems from 2007-2008.