Day lilies again

It sounds to me as though you'll have to dig up the area where they are mixing and create some sort of barrier in the ground between. Others might have better ideas.
I don't have any bluebells but my daylilies and grape hyacinths are in pots for this very reason.

daylilies do pull out relatively easily but don't you find the bluebells die back and then the daylilies are able to do there thing? if you have too much day lily then weed them out. a barrier may help.

I suspect you may have that invasive Hemerocallis fulva. It sends out runners and they can really take over an area. While a few hybrids will send out short runners, the fulva species are notorious for it. They are pretty, but I don't have a single clump (and I have around 1000 daylilies). The easiest way would be to divide them every 3 years. Dig, divide, replant 1 or 2 pieces of 3-4 fans and bin the rest. Or replace it with some of the non-fulva types. For the best flower production, you need to divide the clumps every 3-4 years.

Thank you everyone - is now an ok time to try to dig some out/divide them. Very carefully because of the bluebells! How can I tell if they’re the fulva type ?

they are usually have an orange coloured flower and quite large. the one I have is semi double.. yes you can pull it now but if you are worried about the bluebells wait for them to flower then do it.

That sounds like the ones Thank you very much. I’ll wait till the bluebells have flowered

Please can someone give me a bit more advice?
When the bluebells started flowering I cut down the day lily “shoots” just so the bluebells got some light. But I realise this won’t have solved the underlying problem. When the bluebells have finished flowering should I dig them up together with the root bits of the day lilies and try to separate them out? And then replant the bluebells?
Any more help will be much appreciated

You should do it in the fall. Daylily scapes (the stems with flowers) grow from under the crown of the plants, and if they are disturbed or damaged, you won't have any flowers until later or even until next year. If you dig and separate at least six weeks before the first frost, the daylilies will be fine. I have some Ixia a friend wants that is mixed in with some of my daylilies, and since it is in flower now, I told him he would have to wait until the fall. You also have to wait for the bulbs to recharge for next year before digging them out.