Hi, Passiflora caerulea is only frost hardy, so it's probably down to the cold 'summer' we've had, the 'Constance Elliott' may be in a slightly warmer section of the garden. if the blue 1 is a new plant, they can sometimes not flower very well until they get established, Derek.

I notice that the foliage in the photo is very chlorotic, Thorneyside. Does your soil have a lot of lime in it? You may need to apply sequestrene to get better flowering. Derek is also right in that Passifloras need warmth to bloom, as well.

Thanks Derek. The blue has been there more than ten years so is well established and I must be honest, we haven't had a bad summer. In fact I wonder if it could be where everything is so dry.
My garden is clay/gravel Tugbrethil but this is a raised (brick) border.I have a river at the bottom of the garden so the water table is high in winter months. Our tap water has a lot of lime, that's why we don't use it for drinking.
I wonder if I didn't explain properly. The passion flower is flowering ok BUT one branch has the flowers that are nearly, not quite, all white apart from a small ring around the centre.
Could it be the same phenomenon that has made some flowers change colour this year?

Hi, sorry I misread the question, I thought you meant that you only had 3 flowers on the blue 1, not that 3 of the flowers on the blue 1 had turned almost white, I think it most likely this is caused by the soil being too limey, I would do as Tugbrethill suggests, and give it a feed of sequestrene, Derek.