In Ninewells wood there are some bluebells, most of them are British, actually to be more precise they are Welsh. However there are also a few Spanish bluebells. There are also some daffodils and Aqueliga or Grannies Bonnet, there is a big clump of pink primulas , there is a large patch of a variegated form of Yellow Archangel and to set it all off there are two Forsythia bushes.
I think all these plants were planted by a previous occupant of one of the bungalows located within the boundary of the wood. Now there is strictly nothing wrong with someone planting whatever they like in their own garden, though I would argue that if your garden is close to or surrounded by a natural area then it would be wrong to plant species which could invade the surrounding land or hybridise with near by native plants. However these plants are not in a garden they have been introduced into the woods.
I believe that you can now be prosecuted if you plant Rhododendrons in your garden and they subsequently encroach onto land not belonging to you, though how this would actually be proven is problematical.
It is illegal to remove wild flowers from the countryside, you would be prosecuted if you dug up the bluebells growing in the woods. However you can plant Spanish Bluebells and these will hybridise with the native bluebells and in the long-term this would do more damage than just digging up a bucketful of bulbs and planting them somewhere else.
Another source of non native plants growing in the countryside is people who dump their garden refuse in the country rather than taking it to a municipal dump. This is actually illegal. I will dig up and remove all the Aquilegia plants which are planted on my bit of Ninewells wood and I am gradually knocking back the rhododendrons and Laurel. I would encourage others to do the same to the non native species that they find on their bits of woodland. There are enough wildflowers which are very beautiful without planting garden plants.
To distinguish Spanish bluebells from British, here are some guide lines. Spanish have much thicker leaves, the flowers are more chunky and arranged around the stem, they look like a poor example of a Hyacinth. The pollen is yellow whereas the British has blue pollen. The Flower stalk is upright in the Spanish species and is drooping or nodding in the British species. Hybrids are as you would expect in between and the pollen is green.
Here is a link to a good site that explains the difference between the two species of Bluebells https://granthamecology.wordpress.com/2012/05/16/whats-the-difference-between-english-and-spanish-bluebells/