UK CO2 emissions cut by 38% since 1990 Carbon Brief has an in depth look.
Domestic Cut in CO2 emissions of 38%, ( called Territorial Emissions too) , or even as big 43% CO2e , if non-CO2 GHG are calculated [ banned CFCs & changes in CH4 NOx]
Electricity Generation . The "Dash For Gas" switch from Coal to Gas & Renewable , biggest factor, But Bioenergy is 1/3 of "renewable"
Leaking natural gas which is methane not counted, but believed to be falling, [ could fracking increase methane leaks?]
Average car MPG change from 33 mph in 1990 to 40 mpg in 2017 , which is actually terrible progress & that was driven by EU legislation. A 1959 morris minor or a 1980s Skoda does 40 MPG, so real improvements in engine efficiency have been undermined by selling people bigger cars.
But Shifting Manufacturing over seas Increasing Imports is significant , China is still using coal electricity, so increasing imported stuff increase CO2, If this is factored in, the cut in Consumption CO2 Emissions is only 10% . Consumption Emissions, is defines as CO2 of UK emissions + CO2 footprint of imports - CO2 of exports. Perhaps this is a better measure, but does not incentivize decarbonizing export manufacturing.
See attached graph by Carbon Brief, with 600 Mtco2 baseline added for clarity.