If eating no meat at all is too hard, from a climate perspective eating no beef will have the biggest impact. Eating no ruminants to be specific, but hardly anyone is eating bison/sheep/goat on the regular.
I've only met one person who couldn't go veg, because they had allergies to everything: soy, legumes, nuts.
There's been a lot of obsession with protein in popular culture when in reality unless you're a bodybuilder you don't need a ton and a veg diet will suffice. And there are tons of vegan athletes.
The point I was making is that there is one step even the laziest can take to have an impact: just stop eating beef. Going full veg is better of course.
Is lamb a regular dish or more of a Christmas and special occasion dish? I'm not in the UK so I genuinely don't know. Not sure that you can get lamb at a fast food joint like you can with beef burgers.
And kebab meat is normally lamb. You can get that at pretty much any takeaway chippy in the country, and is traditionally eaten with about six pints of cheap lager.
I'm in the US and can get lamb at fast food joints. Go to any Mediterranean shop for a gyro. Afaik it's even more available in the UK since it's primarily sold as people food, not dog food like the US market.