FMurtz wrote
john west wrote

I had a stamp stuck on an envelope that was not Franked and so thought
had never been used. So i cut around it and stuck it to a new envelope
and posted it. but i got a note from the post office that i needed to go
in and pay extra.

As an experiment i used a stamp that i knew for sure had never been used
but had been stuck on an envelope. So i again cut around it and posted
it to myself and it arrived.

Does the post office have some way of detecting if a stamp had been used
through royal mail even though there is no visible sign of Frank Marks?

Steam them off don't cut around.

Wont help given that they use fluorescent dots to indicate
that its franked and easy to see the fluorescent dots yourself.