If the premise is a platform for launching long range cruise missiles, where does the LO come into it?
How "long" is "long range"? A really long range cruise missile is both large and heavy and requires a pretty big airplane to carry it. Would such an aircraft be affordable?
Separately, Tomahawk is nuke capable and fairly long range. And it can be launched by UK's submarines. Submarines armed with cruise missiles are arguably much more survivable than bombers with cruise missiles. So
if a long range cruise missile is the best weapon (and there are many arguments why it is not), then a submarine may again be the best launch platform for that weapon. In addition, Type 45 destroyers are reportedly Tomahawk capable. What all this means is that there are already multiple cruise missile launch platforms in the UK inventory. So it would appear that an expensive development program can be avoided.