The most pronounced difference is that the flowers of English bluebells are usually only on one side of the stem, whilst the flowers of Spanish bluebells are all around the stem. Some more differences are listed here:
My English bluebells have never flowered, moved them around to no avail, any ideas ?
The Spanish bluebells that come up in my garden are much bigger than the English ones and don't smell so nice. I try and dig them up, keeping the flowers for a vase, but they are not easy to get rid of.
I use glyphosate, doctored with a few drops of washing up liquid as a wetting agent. I use a hand spray (an old glass cleaner handgun) and gently squeeze a few droplets down the V in the leaves, so it runs down to the base. If you have a lot and they are mixed in with more desirable plants you could use a rubber glove on your right hand, dip your finger and thumb into a bowl containing glyphosate solution, shake droplets off into the bowl to avoid accidental dripping, and then rub finger and thumb along the leaves to smear them. That worked a treat for me on MIL's garden a few years ago. It also got rid of ground elder in her lawn!
I've found that bulbs are often sold very young so will flower eventually if left for a few years (had this with frits and daffs), always try to copy what happens in nature so try to give them some leaf mould or lighten the soil. If that doesn't work chuck on a half strength tomato food as a foliar feed.
i have some ink: bluebells in the garden amongst my native ones. can you tell me why or what are they. they are identical to the blue.