I will travel to Thailand with my granddaughter (7), who has a British passort for a holiday

We have different surnames. Hers is Thai

Should I carry a letter from her mother giving me authorisation?

Advice please

As long as she doesn't enter on her Thai passport it's not going to be any problems.

But a letter in Thai from the mother will of course be useful, and a copy her ID, Housebook and birth certificate.

Better be safe than sorry.

 

Yes, take a at least, a signed letter from her mother (in English and Thai), would be good to have her mothers id card  or passport copy on the letter. Also you should have a copy of the kids Birth certificate, (you could take the kids Thai BC, if she has one, as well, just in case as a fall back translation). Will those certs link your Family name to your passport Family name?

 

You will need to check any transit airport requirements as well if not flying direct from/to UK, as the letter may need witnessed by an official...(Some other things dependent if your route is via another country and you are stopping over??)

Do get all paperwork ready, travelling with a minor with different name will flag you in all airline databases.

 

You'll need to contact your airline to hear their requirements.

I was required to have a notarized letter from my grandson's parents stating I had authority to travel with my grandson and manage his welfare while traveling to include any needed medical treatments. Additionally I carried a copy of his birth certificate to validate the names on the letter. However, this was from the USA and only the departing airline asked for the documents.