The surprise move follows a backlash in the Conservative Party against the decision by Mr Clarke and Michael Heseltine to appear alongside Mr Blair at last month's high-profile launch of Britain in Europe, the embryonic pro-single currency campaign.
The actions of the two Tory heavyweights outraged many party members. Constituency activists initiated moves to deselect Mr Clarke and persuade Mr Heseltine to retire at the next general election.
Mr Clarke's promise not to repeat his actions is seen by Tory officials as "the price" of heading off the moves to oust him in his Rushcliffe constituency in Nottinghamshire. His local critics are now expected to drop their campaign against him. Although Mr Clarke will continue to speak out on Europe when he wishes, his retreat may limit the effectiveness of the Britain in Europe campaign in the run-up to the election.
His move has delighted the Tory leadership, which was also cheered by his scathing Commons attack on Gordon Brown after the Chancellor presented his pre-Budget report last week.
Mr Hague enjoys good personal relations with Mr Clarke and hopes to exploit the talents of "heavy-hitters" like him. But there is no prospect of Mr Clarke serving in Mr Hague's Shadow Cabinet, as he would not accept his hardline policy on the euro. Senior Tories say Mr Hague does not want a "purge" of pro-EU Tories but has no objection to local activists flexing their muscles. He believes the row over the Britain in Europe launch shows the vast majority of his party supports his stance on Europe.
Mr Heseltine has not given a similar undertaking to Mr Hague and will now come under intense pressure to quit his Henley seat in Oxfordshire for "aiding the enemy" by sharing a platform with Mr Blair.
Tomorrow Mr Hague will seek to shift the spotlight away from Europe by unveiling a new policy document, Common Sense on Crime, with Ann Widdecombe, the Tory home affairs spokeswoman.
It will promise that a future Conservative government would introduce a specific offence of violence or attempted violence against a public servant while they are at work.
"People who serve the public have a right to do their job without fear of attack," the document will say. "This growing problem has been neglected for too long. We will ensure that the prosecuting authorities are under special instruction to make sure that nothing prevents people accused of this offence being brought to trial."
Half of Britain's nurses have been the victims of a physical or serious verbal assault, according to the Royal College of Nursing, while more than two thirds of ambulance staff have been attacked in the past year.Reuse content