It is because they have been contaminated by the genes from Spanish bluebells so they are no longer pure English ones.
As you can see in the picture the flower arrangement is different too.

Great thanks. Maybe english bluebells will die out like the red squirrel, hope not they're beautiful.

English bluebells can have a white flower ( I guess it's a recessive gene) but it's not as common as the white or pinky mauve versions of the spanish type.

In the 60's there was a bluebell wood near us and there was a pinky one in amongst them. it is also part of the recessive/mutation effect. I have a pressed wildflower book with all 3 colours in from 1968. even at 10yrs old I was a keen botanist :o)

That's lovely Seaburngirl. My Dad gave me a little patch of garden and I cut sticks off his private hedge to mark my plot with Keep Out. My Father was surprised that every one of my 'sticks' sprouted so I then had a nice little clipped hedge. Now, I am ashamed to say that my Scrapbook from when I was ten contained Newspaper cuttings/adverts/pictures of Kit Cars! I didn't have any Brothers so why I developed this interest I don't know. People are most impressed with my Scrapbook as I am 67 this year. No-one in the family was a car fanatic. My car passion has gone on through my life and I am now on my 7th Jaguar. So sweet. Gardening - still very passionate. Nearly all Begonias of different types.
It would be lovely to see pics of one or two of your pressed flowers. I have a bank of damn Spanish 'Bluebells'. I rip most of them out after flowering.