> £40/MWh estimate for wind included gas power generation

No, they're totally separate things. It's not "wind and gas" as a single entity, it's "wind farms supply power to the grid at £40/MWh and gas plants also provide power to the grid at £40/MWh". In other words, it just means they cost about the same which is half the cost of nuclear. There is no 30/70 split as you imagined.

Which makes sense. Scotland gets around 90% of it's electricity from renewables, of which around 70% is wind power. It couldn't possibly do that if your figures were correct.