TRAVIS_TAG not being picked up from Bitbucket tag

I am trying to obtain the tag string from a tag which I have pushed to my Bitbucket repository.

However it seems that the TRAVIS_TAG environment variable is not being set or picked up by Travis CI.
When I echo $TRAVIS_TAG, it is always empty.
I don’t see the tag in the build page either


I can’t seem to find much info on this as I think most other people are using it with Github which might not appear to have this issue.