The vast majority of homes that are easily insulated have been and there are grants available for cavity fill and loft insulation. Landlords are also required to upgrade rental properties. Many of the single skin remainder are in conservation areas or are listed, these would require specialist solutions and we don't have trained installers. Personally I can't believe building regs haven't been updated to make new builds and extensions more efficient. Air source heat pumps are actually the solution here.
Insulating commercial buildings is potentially a much easier win.
A 10 mph haircut across all speed limits makes huge sense. I'd add stop-start technology for every vehicle sold in the UK within 3 years - this technology has been around for well over fifteen years and could have saved at least some of the 40,000 deaths caused by particulate emissions in the UK each year.
Rationing is daft, good luck winning an election on that one. Allowing imports of hormone treated meat is stupid - one of our Brexit benefits though. We already have the option of choosing high welfare UK produced food - look for red tractor.
Less than two hours is regional rather than short haul but the whole aviation sector - short haul, long haul, passenger, freight only make up less than 2%. Airbus recently ran an A380 test flight on 100% sustainable aircraft fuel. Most aircraft fuel is now partly SAF. Domestic flights produce less emissions per passenger mile than a car with one passenger/driver.
How do we know which products have been produced with dirty energy? Without a international legally binding LCA, independently audited process such as the ISO 14xxx series, it is impossible to tell the carbon footprint of any product. The construction industry is well ahead and many products have published EPDs. Even if the law was passed tomorrow it would take five to ten years to train the analysts and auditors. In reality Scope 1 emissions are easier and less subjective and the UK Government have indeed proposed legislation requiring UK Companies to declare their emissions and importantly to deliver roadmaps to net zero.
I'm not sure where you'd put all the trees? Tree planting isn't the panacea many seem to think, bio diversity is key and this includes grasslands, bogs, scrub etc. Indecently cotoneaster is great at absorbing emissions.
Public transport - absolutely, particularly the final mile and urban mobility and many cities are experimenting with this but again there are infrastructure and skills gaps. Look at some of the issues with e-scooters.
Massive offshore wind and hydrogen is happening. But there is still a huge amount of research and development required - you don't just pop to the shops to buy a 200 m diameter turbine. And much like insulation the skills and materials supply chain cannot be switched on over night.
Any proposal needs to be realistic and meet public approval - unfortunately while intentioned many of the proposals put by some of the campaign groups would do enough to meet net zero targets without massive damage to the economy and peoples lives. And while we borrowed our way out of COVID there is no way we could borrow our way out over a short period time while simultaneously trashing the economy.
Net zero by 2050 is challenging but doable, it would be impossible if we all as you suggest.