Confusion tracking status

Hi,

I have a letter that is being posted to me from Gibraltar to Singapore. The tracking # is RT601375156GI and is on the international tracked and signed service.

The latest tracking from Royal mail has "Item leaving overseas" and the Gibraltar post tells me a waybill has been assigned and a number SQ319(?).

Can anyone help me understand what is happening with this letter?

SQ19 is the flight from Heathrow to Singapore - I am guessing it's being loaded on to that aircraft.

Otherwise, if it has arrived in Singapore but isn't yet on singposts database then its likely in customs.

SQ19 is the flight from Heathrow to Singapore - I am guessing it's being loaded on to that aircraft.

Otherwise, if it has arrived in Singapore but isn't yet on singposts database then its likely in customs.

Thanks for this info.

I am trying to understand - is there any way to tell if it has definitely left the UK? I was provided with a tracking number and also with a rather long number beginning with GBLALA.
When you say it is likely in customs, do you mean UK Customs? I'm surprised that a simple letter has been sitting for so long!

Thanks again.