Jon,
Did they give you a TNM staging and discuss their finding regarding advanced staging characteristic such as extra capsular spread(you might need a PET/CT for this), nerve or structural invasive considerations?

50/50 really isn't what you want to hear so you need to get ready for a fight and have a team and CCC that can take you all the way.

What is their proposed treatment plan, optional consideration and why.

Is the BOT tumor surgically resectionable and/or can they shrink it first with an induction chemo cocktail.

Is this Thailand Cancer Center affiliated with a major US or European CCC's?
Do they follow the multidisciplinary approach - tumor board, etc..?
Are they well regarded and do they have the up-to-date world class expertise and technology in Head & Neck cancer treatment?
Do they see and treat at least a couple hundred cases a year?
Can or should you return to the UK?

I would also suggest you have them test your slides for HPV, although I understand that NORMALLY HPV expresses obvious and large lymph nodes before the primary get big and invasive.