you might be questioned, I have flown from London few times Manchester couple times and from Brunei and never been questioned it’s up to him what he wants to do,
no idea it was linked on a pattaya group I’m in which I can’t find it on and unfortunately it’s a private group, you should search YouTube maybe you will find it
Phone the embassy they will guide you through it, you need to book your flight and have your medical certificate either same day as flight or day before
You also need insurance too there’s a video on YouTube of a guy that has done it explaining it all hope this helps 👍