Are you saying they have all been ring barked? has each one been cut all the way round at the base? if it were pest damage ie rabbits you would see signs of gnawring, has their been any difficulties with your neighbours, any disputes over this hedge? believe me i could tell you some storys about neighbours and garden sabotage, the most common being poisoning, and in the past creosote painted onto the foliage of conifers etc.

Has anyone been using a strimmer to cut the grass around the trees? The line or blade could cause ringbarking.

And rabbit and rodent damage can still look very much like the work of a pen knife--those front teeth are incredibly sharp!

Thank you everyone for helping me - i had never heard of ringbarking! I Googled ringbarking images and it's not quite the same - i don't get on with one of my neighbours but my shrubs were not on our joint fence so i can't see them sabotaging me (i hope). Anyway whilst looking on Google i noticed that bank/field voles kept popping up and it seems to make sense to me that's what it is - only problem now is how to get rid of them - need a cat but have 3 dogs! No strimmer used at that end of the garden as there is no grass there. Once again, thank you all for your help, i think the mystery is solved if not the problem :o)

I can tell you how to discourage field voles from bitter experience, ads they killed a 12 foot cotoneaster by eating so far through the base of the trunk that it fell over, and then they started on another shrub. I tried bandaging the gnawed area - no good. I put used cat litter round it, but no good. So I sprinkled hot chilli pepper round it and have had no more trouble anywhere. You can get large bags from Asian shops, if you have any within reach, which is cheaper than little supermarket packets.