If they promoted nuclear while they were in government they would have been expected to actually build it, though.
Now that they're in opposition they're free to run a fact-free pro-nuclear campaign to undermine solar and wind without the obligation of building anything.
It's not like their real policy of "rich people should get richer" is going to get them a lot of votes from 90% of the population, so they need something to pretend to stand for to bring in the votes.