Now you've gone on a weird tangent where instead of talking about the topic on which I pointed out the numbers don't work (stockpiling gas in June so as to not need it in January), you've decided that for some reason the UK's goal needs to be making exactly the same ratio of extra
electricity as as the fraction of Russian
gas they used to import.
But those aren't comparable numbers, which will be why you've got this ludicrously small result. Even with the weird choice to replace specifically Russian gas in the UK (What about elsewhere? What about the huge price increases? What about global supply concerns?) you need to replace the gas not some portion of electricity. So that means you need to stockpile... drum roll... 5.6 billion cubic meters of gas.
But gas is a physical material, you need to keep it somewhere and the UK doesn't own storage for 5.6 billion cubic meters of gas.
It might seem like they must have more than that, but imagine what it would look like, imagine a 20km by 20km box, 14 metres high, that's the internal dimensions of the storage you're imagining.
The UK did own a noticeable fraction of 5.6 billion cubic meters, not enough but a fair start, the Rough storage site. Rough is actually gas wells which are dry, re-purposed as storage. However, the UK government didn't want to pay for this, so after it was sold into the private sector the owner decided they weren't bothered and it was moth-balled. Once emergency payments were forthcoming, a fraction of Rough that was in least bad condition was re-opened for this winter. Again though, even the whole site if magically restored to 100% service would not store 5.6 billion cubic meters, that's just a lot of gas.