The Stratford on Avon MP criticised Gillian Shephard, Secretary of State for Education and Employment, for making the suggestion. "I've heard she has lowered the tone of the discussion, calling me vindictive and suggesting that I am in mental turmoil. "People will have to form their own judgement. I think her comments are silly and unfortunate," he said.
Mr Howarth also criticised Mrs Shephard for failing to secure extra resources to improve educational standards. But he gave her "marks for trying" to stop Michael Howard, the Home Secretary, appealing to the "worst nature" of the Tory party by seeking to make employers screen immigrants. The MP went on to dismiss newspaper reports linking his move to the recent breakdown of his marriage. "It was, I suppose, par for the course. Some of what the Tory press has been saying is very vicious."
The fresh outbreak of acrimony came as the Tory party cranked up attempts to bury the issue before the conference gets under way today.
Sir Norman Fowler, a former party chairman, dismissed Mr Howarth's claim that up to 40 Tory MPs shared his feelings about Conservative policies. "It's just a two-to-three day wonder that will not overshadow the conference," he insisted.
Delegates also insisted that Mr Howarth's action had not blighted the conference. They said the people who had been let down were the electors of Stratford on Avon who had thought they were voting for a Conservative MP.
It emerged yesterday that Frank Dobson, Labour's environment spokesman and part of the party's "rebuttal" team in Blackpool, had voted for a Private Member's Bill in 1981 which sought, unsuccessfully, to force MPs who crossed the Commons floor to immediately re-contest their seats in by-elections - a course Mr Howarth has refused to take.
"In a Private Member's Bill you can decide whichever way you want," he said yesterday. "It is for Mr Howarth to decide. I heartily welcome him into the parliamentary Labour Party."
Mr Howarth said he could understand the criticism from constituents that he did not immediately resign the seat.
"But if you look at our political history over the last 20 or 50 years you will see that convention and practice in our constitution do not require there to be a by-election if the sitting member changes his allegiance.
"It has happened on many occasions. I am aware of some 60 instances over the last 60 years," he said.
However, the decision was clearly causing anguish to some on the centre- left of the party. Peter Luff, MP for the neighbouring Worcester constituency, wrote to Mr Howarth urging him to reconsider.
"To claim, as you did, that the Conservative Party has betrayed the so-called 'One Nation" tradition is, as I am sure you know in your heart, simply wrong," he wrote.