I started following this guy hoping for some sound legal advice... but I have yet to hear anything other than rambling which is highly confusing when you're trying to know the answers! I commented on the video, yet it's magically dissapeared!
I needed to keep my UK number when I moved here, mainly for mobile banking as my bank doesn’t accept foreign numbers, I switched to Lebara and pay something like £4 a month. Just remember to regularly send a text message to keep it active. I just text my Thai number once a month!