Rob's right as any ship with a UK port of registry can be commandeered by the Government in time of war if needed. In the unlikely event Britain were to face another Falkands type situation requiring large scale maritime forces then it is entirely feasible that both QM2 and QV could be taken up in the same way as their illustrious predecessors and used in a troop carrying capacity. I say unlikely because it is doubtful there would be sufficient RN capability available to mount another campaign of the magnitude seen in '82 but yes, it's entirely possible should the need arise.
With regard to Canberra's much publicised dig at QE2, although light hearted there was however more than an element of truth in the comment. While QE2 remained in relatve safe waters well away from immediate danger, the 'Great White Whale' (as Canberra was affectionally known), was in contrast, very much in the thick of things, spending time in San Carlos Water (or 'Bomb Alley' as it came to be known for obvious reasons). It's widely believed that QE2 was kept away as any attack upon her would have been a huge coup for the Argentinian forces, not only because she was a British ship and a prestigious one at that, but because of her being named after the Sovereign (even though we know that's not strictly correct).
That's not to suggest QE2 was totally immune from risk for that was certainly not the case but it is true to say that she was clearly not exposed to the same extent as her rival. Irrespective of that however, both ships returned safely home having played their part with distinction and served their Country with pride, just as QM2 and QV would if called upon. Let us hope they will never need to do so.