Hi
Hoping somebody would not ask that question lol. Hopefully this explanation is clear
The over 10 year issue arose because between 2001 and Sept 9th 2018 any period of unused validity could be carried over at renewal, up to a maximum of 9 months
So a passport issued on Sept 9th 2018 could have an expiry date June 2029 (10 yrs. +9months) so anybody using it now could fall foul of the 10 yr. rule.
In fact their passport will expire Sept 2028. 10 yrs from date of issue
Since Sept 10th 2018 passports have only been issued with a maximum of 10yrs for adults, and 5 yrs. for children.
The only exception to this, is travel to Ireland, where a UK passport need only to be unexpired.
Geoff