Thanks for replies. in answer to the dimensions question, the space i have to deal with is about a metre or so wide (part of the border plus the existing hedge access strip) and I guess about 5m long roughly, at least for the bit of boundary behind the border. i don't know yet what I want to do along the rest of the boundary which runs behind the veg plot and a utility/composting area and any replanting will only have the width of the current hedge to make use of (around half a metre on my side of the boundary).
Since posting i have done some more research and found information about native wildlife friendly shrubs that are garden worthy and grow well in or are indigenous to the area. Not sure if all that I like are suitable due to size but the ones i like the look of are; hazel, hawthorn, spindles (euonymus europeaus), holly buckthorn, blackthorn, elder (already got one of the wild sort), guelder rose (viburnum opulus) and cotoneaster (one of the taller large leaved species). I discounted others such as willow and native dogwood as being unsuitable for the site (too dry).
Of course i could go down a more ornamental route and some of your suggestions are interesting, particularly pyracantha which I do have in the garden and is a particular favorite of the local blackbirds when 'in berry' (one was laden this autumn and one pair of blackbirds went mad over it and stripped it in no time). i have a couple of young firethorns that i could move, or i could propagate some afresh.
I have seen this problem coming for about a year now. Back in the spring i replanted the border in question and rather than using all herbaceous as before i did add 3 shrubs at the back for structure more than anything else but i guess at the back of my mind i knew the hedge would not last many more years. By planting possible replacement shrubs now while it is still there will mean they will be well grown by the time the hedge is removed. I am just not sure now if i have used the right plants from a wildlife/bird point of view. I planted Flowering Currant, Eleagnus and Cotinus. These will be added to with what ever i decide upon as a result of research and this thread.
I would appreciate any thoughts or comments on this.
Thanks