For a first international experience, it may be wise to try something other than the job. There are indeed other solutions to go abroad, solutions often more accessible, more advantageous and more formative. Before leaving for work abroad, you can start by doing an internship (even outside your university course) or a voluntary service. This will enrich your CV, reassure your future employer on your adaptability and fluency in a professional or quasi-professional context, and will give you the benefit of a first non-native experience for teaching in Thailand.
Go on the spot
Can you find a job abroad while staying in UK? Yes, undeniably. However, you will naturally increase your chances of finding the offer of your dreams by visiting the site. Teaching in Thailand is really a challenging job but once you try your foothold there, the environment will give you an idea of what to expect so that you can prepare yourself accordingly. It is probably easier to find a job (very) qualified from UK than a summer job, a student job or a job that does not require any special qualification. Indeed, by definition, these jobs are accessible to the greatest number and an employer will only have to make an announcement to receive hundreds of applications. So why would he bother and take the risk of bringing someone from abroad when he already has everything he needs at hand?
To cope with the competition, it may be useful to visit the country especially if you choose a European country bordering France. This certainly requires an initial investment to pay for transportation and housing for a while, but, whatever happens, if you want to work abroad, you will have to travel at some point. With active research, if you have the right qualities, you should find your happiness more quickly than sitting behind your office in England.