The Worldwide up to 40 grams stamps can now be used on packages up to 100 grams in weight.
These self-adhesive post & go stamps are 100% valid for postal however the Royal Mail issued them with the backing card flush to the stamp perforations which makes the stamps very awkward to remove from the backing card. In fact you need have very good eyesight and very good nails to stand a chance. Hence why we are selling them off at a large discount to the face value.
We do occasionally use these stamps ourselves on Worldwide packages up to 100 grams and rather than trying to remove the card back we just use a glue stick on the card back which does the job fine. All of these stamps originate from definitive stamp presentation packs issued by the Royal Mail and are 100% genuine.
Although it only says up to 40 grams on the stamp the new Royal mail rates from 30th March 2015 means these stamps now cover you for letters up to 100 grams.