Some questions first
1. Where are you in the UK?
2. Are the yellowing ones all together, or intermittently spaced between the other 7 which are alright?

Hello! Also which Bay do you mean ... Nobilis, sweet aromatic bay; laurel bay, or willow bay which has yellowing leaves that show their best in autumn/winter?

Well, I'm assuming Laurus nobilis - I don't call any other plant Bay other than that one, Avkg47 - I've never heard the terms laurel bay and willow bay, must be regional.

Hi Bamboo in answer to your question, i live in Derbyshire,and the 7 yellowing ,are all together.
Also in answer to Avkq47 they are Laurus Noblis

I'll assume you're not in drought then, given where you are. There must be some difference in the conditions for the yellowing 7 compared to the other 8, so think about what that might be. For instance, are the 7 on the end, in open ground, much more exposed than the other 8? Are they planted on a downward slope? Is there a fence or other shelter for the 8, but not for the 7? Are the yellowing 7 in deep shade? Photographs of the run of plants otherwise might help, showing the surrounding area - which way does this border face?

Hello Bamboo ... Laurus nobilis is also bay laurel, bay tree, sweet bay. Angustifolia is also commonly called willow bay, so may have been an option for identification, especially as the 'aurea' variety has yellow leaves in winter and spring. Very unlikely that Laurus nobilis leaves are yellowing, unless the roots are severely drying out, and the leaves are dying?

Sweet bay I've heard, and Bay tree just means laurus nobilis as a tree, as far as I'm concerned. Never heard a willow called a bay as I said, but I've no patience with common names, frankly - from what you've said, it now appears there are at least 4 common names for Laurus nobilis rather than the 2 I already knew about, all of which may mean other plants. The term Bay is acceptable, doesn't mean anything else, to me anyway, and we all know bay leaves from cooking.
Laurus nobilis leaves are as likely to yellow as any other plant's if there's something wrong.
Rachael, I realise I got the numbers wrong in my last answer - I keep referring to 7 yellowing and 8 healthy, obviously that should be the other way round, lol!

Hi Bamboo and Avkg47, thank-you very much for your help. I'm thinking,it could be lack of water,there is no fence in front of them,but they are slightly in the shade in comparison with the healthy ones,so i'll try watering them more frequently, whilst allowed lol!! The border faces north.

Are the ones which are suffering up the eastern end of the border? And is the border open, in other words, there's no fence on either side of these plants, so they're fully exposed? As for the shade, what's causing the shade - are the dodgy ones too close to some overhanging trees or shrubs which take up root room and sustenance in the soil? As for watering, the ones with more shade should be damper than the ones not in shade - the ground dries out quicker where there's sun. On the other hand, if there are large, competing plants nearby, the soil may be dry.

Hi Bamboo, the border is completely open,with no other plants around it,the shade is caused by a tree on the grass verge,outside our house (which belongs to the local council).Yes I agree about the watering,just grasping at straws.

The reason I asked if the yellowing ones were up the eastern end of the border is exposure to wind during winter particularly. If they catch cold easterly or northerly winds, this can cause yellowing and general poor growth in bay.

Maybe that's the problem then,thanks for your help.