I still find it awe-inspiring to think of the state of the nation you inherited and the immense achievements of your governments. Getting the country to live within its means, bringing the trade unions within the law, rolling back the tide of state ownership, standing steadfast with our allies in the cold war ... but above all giving the British people back their pride and self-belief. The whole country owes you a huge debt.
The tone of the letter will raise hopes within the party - and fears outside it too - that the Conservative response to the recession may see Cameron more willing to present himself as a Thatcherite.
Cameron's treatment of the Thatcher legacy has provided a masterclass in political ambiguity. According to mood and audience, his "progressive Conservatism" has been presented as both break and continuation of the Thatcher legacy.
Take what was probably his most important speech so far this year - at Davos.
The Guardian reported that Cameron hails Thatcher in his call for 'truly popular capitalism',
The Daily Mail reported that Cameron calls for 'moral capitalism' in move away from Thatcher.
Or take the Cameron soundbite which was used consistently from the start of his leadership with the clear intention of signalling his distance from the Thatcher legacy.
Cameron has said, as often as possible "There is such a thing as society; it is just not the same as the state".
He was not the first to make that argument. The source of the quotation is a revealing one.
And to set the record straight — once again — I have never minimised the importance of society, only contested the assumption that society means the State rather than other people.
That was Margaret Thatcher in her Keith Joseph Memorial Lecture on Liberty and Limited Government of 1996.