Strange Problems Posting Abroad, Knowledge Sought

Hoping maybe there is someone out there making regular use of the Thai postal system for overseas shipments that can shed some light on this problem.

I have been having regular consignments posted from Bangkok to London. These are sent by air as International Registered letters (or parcels if they are over 1 kilo). Here is the problem, a parcel arrives in an average 5-7 days.

The letters take a minimum of 3 weeks !!

That is on the last 4 that have been posted. They hav,nt been opened or subjected to customs delay. The track and trace system shows them as having been posted....and then nothing until 3 weeks later.

If I have them sent by ordinary airmail, non-registered, they will also arrive in an average 5-7 days. I have tried talking with Thailand post, they are helpful but they can't explain it either.

Sometimes I do need to have a signed for delivery and EMS is too expensive for small consignments.

So if there is anyone out there sending stuff abroad regularly, maybe as part of their business who either has or has not experienced similar probs with their post I would be interested to hear from them.

Thanks.