My 10 year old son has both Thai and British passports.

I don't see him using the British one soon, and having seen the price of a new one in another thread, I am wondering what would happen if it were allowed to expire.

Would he have a problem applying for a new one if the old had expired years previously?

There's no urgency in applying; my Grandfather is British (born in Boston) and travels rarely. When he got a new-style one a few years back (he was in his early 80s) he realised he hadn't had a valid passport for most of his 70s! He just never left Blighty.

If your son has his birth certificate he'll have no problems.

One thing to think about, however; passports will only ever get more expensive.....and....I think the cost is fixed in sterling and then converted, so if bahts are strong now might be a good time.

Not a problem to obtain again later if needed. For some countries, however, it is easier to enter using British passport than Thai passport. Returning to the UK, for example, would require a visa if using Thai passport.

Thank you