As I say, the article on R4 this morning seemed to suggest that across the commonwealth there are plenty of people willing to put their hands in their pockets to buy the Queen a new boat. If there is a shortfall (and it would be wise to assume that there will be) why is there an assumption that it would only be the British taxpayer who would make up 100% of that shortfall? After all, this would be an asset belonging to the whole commonwealth - surely the other members of the commonwealth (most of which aren't in the grip of a fiscal maelstrom) could also, reasonably, be expected to contribute to the costs.
To look at this from another perspective - and not one that I particularly agree with but I think is worth considering nevertheless - if the appeal raises half of the necessary £60 million and the British government alone offers to make up the remaining outstanding £30 million, the shipyard chosen to build the ship would win an order for £60million worth of work which 'only' costs the government £30 million. If this was a regional regeneration project, £30 million would be very small beer indeed.
For clarities sake, I'm neither calling for, nor in favour of government subsidising industry in the name of regional regeneration, but if the project had been expressed in these terms, it would make some sort of sense.