Ah, but PN, the reason it's being assembled in Rosyth is because Cyclops fannied about for years (~2002 to 2006) refusing to fund the ships because they were going to cost £3.2Bn, vice the budget (set for the 40000te concept ships in 1998) of £2.7Bn. During that time, the only other facilities capable of building that size of ship were shut or substantially downgraded (eg Swan Hunter, Harlands).
In all the arguments about the lock-in clause of the contract, people need to recognise the enormous pressure applied by Paul Drayson between 2006 and 2008 to get the remaning shipyards to merge (VT, BAE). Of course they were going to want some sort of guarantee back for that - the government and MoDs track record was not exactly inspiring.
Then don't forget that the programme was shifted two years right to fix an in-year overspend at the cost of £700M!
It would have been much easier cheaper and less grief to have understood and funded the change in original budget back in 2002/2003, although that wouldn't have fixed the obvious issue with tying in to a one-horse race for the aircraft......