For her, the decisive issue was the unacceptability of losing the monarch's head from the stamps issued by a private company, which might not worry Morning Star readers but it could prove a bridge too far for many government supporters.
Previous attempts to privatise this well-loved institution - not least the effort under new Labour led by business secretary Peter Mandelson - have faltered in the face of an exceptionally broad coalition of opposition.
The Communication Workers Union has always been at the heart of such coalitions, but they have been swollen by a plethora of groups and individuals that feel threatened by this privatisation too far.
Former postal union official Tony Clarke played a central role in the House of Lords last time round, arguing alongside ermine-clad countryside campaigners, business representatives, religious leaders and monarchists to defend the public mail service against the "public bad, private good" zealots.
Throughout Britain MPs from all parties were deluged by demands that they oppose this shoddy manoeuvre.
The latest assault on our publicly owned Royal Mail requires a similar inclusive mobilisation.
Opponents of privatisation will have their own reasons for doing so. There should be mutual respect for individual motivations.
Royal Mail staff know what is in store for them, having witnessed other sell-offs over the past 30 years.
Jobs will go, working conditions will worsen and pensions will be cut. This will not be assuaged by the contemptible bribe of 10 per cent of Royal Mail shares being offered to the 150,000 workers to buy off staff hostility to privatisation.
CWU members have indicated overwhelming support for strike action against privatisation in light of the effect it would have on their terms and conditions.
David Cameron claims widespread public support for the government plan to sell off a majority stake in Royal Mail, which suggests that he is confusing public consultation with hobnobbing with City bankers who stand to gain around £30 million as the price for handling this nefarious operation.
He must know that opinion polls indicate around two-thirds public disapproval of Royal Mail privatisation.
His pledges on universal service, uniform pricing, six-day deliveries and free service for the blind and troops serving overseas are repeats of the pie-crust promises heard before earlier sell-offs.
Once privatisation goes ahead, new private owners will petition to drop six-day deliveries or introduce price differentials on urgent commercial grounds.
Given experience of other privatisations, they will be successful while abandoned rural communities will be left to whistle for Cable's promises.
Royal Mail does not need to be flogged off to modernise, to raise investment and to be profitable. It is doing all that in the public sector.
There is no pressing need for the conservative coalition to sell Royal Mail other than its desire to build up an election war chest to offer tax bribes for April 2015.
Royal Mail privatisation will enrich a small number of speculators, but it will degrade the lives of the vast majority.
Every trade unionist should signal antagonism to this scheme by signing the saveourroyalmail.org petition and supporting efforts by campaigners to raise public awareness and defeat privatisation.