The former Hong Kong governor's decision to sign the letter to the Independent was seen by his friends as a move to put down a marker against the Tory leader's scepticism over the single European currency.
"He has made it clear he is not trying to catch the ephemeral mood of the Tory party. It indicates to William Hague that there are forces who are more contemporary than Geoffrey Howe that are not prepared to see the Tory party hijacked by the Euro-sceptics," said one senior Tory who signed the letter.
Mr Patten, who recently bought a house in west London, where he spent New Year before planning a return to his farmhouse in France, has told allies he is not making up his mind about whether to seek a seat in the Commons until the autumn, when he has finished writing his book. The former party chairman has his own "Hurdish" doubts about the euro but regards the euro debate as the most important issue facing Britain and Europe since Bretton Woods, and it is "not tenable" for the Tories to suspend any decision for 10 years.
Lord Howe was behind the decision to organise the letter, and he persuaded Mr Patten to sign it last Friday. The former foreign secretary has taken a leading stand in warning the present leadership of the Tory party that the euro enthusiasts have been silent too long and will not stand back while the party is taken over by the Euro-sceptics around Mr Hague.
Lord Howe delivered his first warning in a letter to Lord Parkinson, the party chairman, before Christmas, described by his allies as "stinging". The letter warned the party chairman that they were prepared to speak out to challenge Mr Hague's policy of ruling out a single currency for 10 years. That was followed by a meeting shortly before Christmas at Central Office with a delegation of the officers of the Tory Positive European Group, led by Kenneth Clarke, to leave the party chairman in no doubt that they meant business.
Those who attended included Sir Ray Whitney, a right-winger who is pro- Euro, Ian Taylor, a former minister and David Curry, the former agriculture minister. Both Mr Taylor and Mr Curry had resigned from Mr Hague's front bench in protest at his line on Europe.
Some members of their group warned Stephen Dorrell, the shadow education secretary, that he could not remain on the fence. Mr Dorrell and Sir George Young, the other pro-Euro spokesman in the shadow cabinet, decided to stay, but are now under pressure to speak out. They were joined by Michael Jack, another pro-Euro Tory, who replaced Mr Curry. The underlying question about the letter is whether it will lead to a final split in the Tory party, with the pro-Euros leaving to form an independent rump on the Tory benches.
They could follow Peter Temple-Morris, who is now an independent sitting with Labour, and Hugh Dykes, who defected to the Liberal Democrats after losing his seat.
The introduction of voting by proportional representation for Westminster elections would almost guarantee a split. But Sir Edward Heath has made it clear he is staying put, whatever happens.