Unpopular, but I'll be honest. I'm from the US and live here now, but spent some time in med school in the UK.
Nothing you do on a personal level in the UK is going to impact the environment in any meaningful way.
I've had my air con on since April. All day every day. We have central air in half of the house, and 2 window units in the other half. When I turn it off, the heating will go on for large chunks of the day. DH and baby DS both home most of the day on most days.
This isn't a 'just me' thing. This is everyone I know in the Mid South.
When we go to the grocery store, we don't walk. Even though the store in 10 minutes walk away, the area isn't built for pedestrians. There's no walkway.
Almost no one walks anywhere. Public transport is almost non existent, and used by the poorest of the poor, or some of the worst people only. As a woman I would never feel safe on a bus.
Plastic bags for shopping are everywhere and abused so heavily. Baggers regularly add 1 item per bag.
And this is before I talk about how much industry uses and wastes.
I'm not saying this is right, I'm just saying if you're uncomfortable at home 'for the environment' don't be. The US absolutely has it covered in ruining everything and that's not going to change. And I don't even think we're the worst country.