Use passport 1 with the immigration. Just show passport 2 when you check in for the flight so the airport staff see you have the correct visa. They won’t be looking for Thailand stamps or care if you have two passports.
Please post data like this in future if you wish to put forward an argument. As you can see by the empirical data, your silly picture is completely and utterly wrong.
with all due respect, you commented that the NHS is on its knees. I was merely pointing out that the reason for that is the serious underfunding over the last 14 years by the Tories. Not by asylum seekers, which are not ‘illegal immigrants’. But that’s for another conversation if you wish to go there too.