We are always warning people of the issue of the spanish bluebells (Hyacinthoides hispanica, syn. Endymion hispanicus or Scilla hispanica). The Spanish bluebell is the worst enemy of the native bluebell because it will hybridise with it; when it does, because its genes are dominant, the traits of the British bluebell disappear within a very few generations. A stand of Spanish bluebells left to seed in a British bluebell wood will, in a few seasons, overwhelm and replace the choice native plant. You might think, “So what? Surely a bluebell is a bluebell,” but the wild native is special.
Can one actually buy the British version?
You can indeed look for bulbs of English bluebells (Hyacinthoides non-scripta. At present you will only be able to buy them as potted plants but at least that way you can check they are truly the native species although more costly.