Ehhh. From what I understand, it's just not feasible. You're going to spend more CO2 doing this than you'll recover from the trees unless you handle everything in-house. Remember, cuttings/needles are pretty dense/heavy, especially since they won't be dried. You'll also somehow have to gather the trees, I don't know about places in the UK but here it's not exactly super cheap (for customers or the companies), especially when you consider all the gas needed to pick up, transport, then the labor for unloading/processing.

I remember talking to someone who's done research on this specific thing and from what they found, it just wasn't economically/environmentally feasible. Especially since the holidays are the major time you'd be able to get them. Maybe new advances/discoveries will change that, who knows.