The best metal production 1911s are generally thought to be the KJW. Their MEU version would be my choice purey because It has better sights than the classic version.
KJW 1911s take both green gas and CO2 mags. Because the mag does not have much gas capacity and the slide is heavy, you will probably get better performance with CO2, though I don't like it myself. The green gas mags are OK in warm weather but you'll probably have to refill each time you empty the mag of bbs. Not a problem if you aren't a skirmisher.
The problem is that KJW pistols aren't as widely available in the UK, though this retailer stocks them..
https://www.bullseyecountrysport.co.uk/kj-works-1911-meu-airsoft-pistol-kp-07-black-green-gas-version-15744-p.asp
You might also consider a hi capa. It doesn't have the classic 1911 appearance because of the grip area and fat magazine, but it is pretty close. The KJW KP05 is the closest you will get to a 1911.
https://www.replicaairguns.com/posts/2013/2/16/kjworks-kp-05-1911-hi-capa-blowback-airsoft-pistol-table-top.html
,Armorer Works also makes hi capas which will run on both green gas and CO2,, and some are available with red or blue slides. They are professionally done in the factory and look much better than ones that have been spray painted by a retailer.
I had one with a blue slide and it was an accurate and nice looking gun. I bought it from here: I would be prepared to buy another.
https://www.geniestuff.co.uk/hx1105-airsoft-pistol-armorer-works-hi-capa-gbb-blue--red-580-p.asp
I think you might want to consider a hi capa rather than a 1911 if you want it for shooting at home or in the garden. They take up to 30 bbs and in warm weather you can get a couple of mags out of one fill of gas. And they actually look good with coloured slides. With a 1911 you will be lucky to get 20 shots, even in hot weather. In cold weather you find their performance underwhelming. The mags, like the grips are just too slim to hold enough gas. And coloured slides don't look so good on the 1911.
Build quality of KJW and Armorer Works is in my opinion superior to KWC, and you can get replacement parts for them.