Thanks for your reply.
So I should be able to deduct 30% ( rental income expenses allowance )
Then get into the graduated scale.
0 – 150,000 Exempt
150,000 – 300,000 5%
300,000 – 500,000 10%
500,000 – 750,000 15%
750,000 – 1,000,000 20%
1,000,000 – 2,000,000 25%
2,000,000 – 4,000,000 30%
Over 4,000,000 (see note 1) 35%
All assuming, I can't just forget it all because of the dual tax agreement between Thailand and uk.
That's all a bit of a gray area to me at present.