Mixed about this.
If ITER works, then it will all be a huge waste of money.
At the same time, whilst it is expensive, we should be building this stuff whilst oil is cheap.
ITER is many years away, and even if it does work, it will take time to develop the following generations of fusion reactors.
Current nuclear fission is worth expanding of course, and we need to do this ASAP. And employ a new re-processing system such a PRISM.
Tidal has some potential expansion, but the reason that the Seven Bore didn't happen was largely down to its unique design. In other words, its not something you can roll out across the country's other estuaries etc, as each one would need a specific design, which would add to the cost. And its still intermittent, albiet preictable.
The reason that wind has enjoyed such expansion is that it is repeatable across the whole country (and world). You get a small number of designs, and replicate it thousands of times, and save a huge amount of dosh.
The subsidies that renewables enjoy apply to both, so that isn't the issue here.