Can a teenager  (19 year old) leave Thailand on a new British passport when he entered on a Thai one a few months back?

 

No, he should leave on the passport he entered the country on, so he should clear Thai Immigration using his Thai Passport.

 

I suspect your concern is the lack of an appropriate visa in the Thai Passport, in which case show the British Passport at check-in, the Thai Passport to clear Immigration, and then the British Passport to board the aircraft and at the final destination, it's all perfectly legal.

 

I'm assuming the flight ticket is in the same name as his British Passport? 

5 hours ago, theoldgit said:

No, he should leave on the passport he entered the country on, so he should clear Thai Immigration using his Thai Passport.

 

I suspect your concern is the lack of an appropriate visa in the Thai Passport, in which case show the British Passport at check-in, the Thai Passport to clear Immigration, and then the British Passport to board the aircraft and at the final destination, it's all perfectly legal.

 

I'm assuming the flight ticket is in the same name as his British Passport? 

sadly he has lost his Thai passport and his father won't sign for a new one - which they say he must do.

20 hours ago, Notadoctor said:

sadly he has lost his Thai passport and his father won't sign for a new one - which they say he must do.

I believe the age of majority in Thailand is 20yo. So, presumably, the need for the father to sign the passport application will fall away when he reaches that age.

8 hours ago, dabhand said:

I believe the age of majority in Thailand is 20yo. So, presumably, the need for the father to sign the passport application will fall away when he reaches that age.

Doesn't help now though....apparently the mother can't sign.....a bit of sexist legislation embedded in Thai law 

11 hours ago, dabhand said:

I believe the age of majority in Thailand is 20yo. So, presumably, the need for the father to sign the passport application will fall away when he reaches that age.

Actually as he is under 20 he his still regarded as a child under Thai law.  Therefore to obtain a Thai passport both parents have to present themselves at point of application.  However this hurdle can be overcome if the Mother could get an affidavit from the boys Father giving permission for the Mother to act on his behalf.  But guess here the Father won't play ball

seems to me there are 4 choices,

get the father to agree  or a work around

find the lost one

remain in Thailand until 20

maybe if the uk passport was issued in Thailand and its the first use, but i think its getting the immigration officer to play ball

 

maybe a land border crossing, using uk passport would be easier if as point 4 above

14 hours ago, Notadoctor said:

Doesn't help now though....apparently the mother can't sign.....a bit of sexist legislation embedded in Thai law

 

Both parents have to sign; unless one of them has been granted sole responsibility by an ampur or a court. So the situation would be the same if it were the mother refusing to cooperate.