Whether you like it or not, the UK still requires oil and gas in its energy mix, and will continue to require it for another decade or so. The options are to ship it in from the middle east, US, or Russia. Or, we can source it ourselves from the North Sea. Getting it ourselves will actually have less CO2 emissions as we won't be shipping it halfway across the planet.
Not if the country went on "war footing" about the climate catastrophe and took measures to ensure that budgets were redirected into eco-investments (eg. stop spending £3 billion a year on the maintenance of 50 trident missiles). Radical investments in things like tidal power, completely free public transport etc. Where there's a will there's a way.
Except, how long will it take for this expansio to come onstream, and how expensive in terms of CO2 emissions will the infrastructure manufacturing be?
That is assuming that by extracting it ourselves we are at least equally reducing how much is being extracted elsewhere…. Which obviously isn’t the case. This will take carbon that’s currently trapped under the ground and release it into the atmosphere.