Depends how bad the shrub looks overall - this appears to be Escallonia leaf spot, a fungal infection which is specific to these shrubs. If the shrub is generally healthy, you can cut back hard, but always remove any fallen unhealthy leaves as soon as you see them, and pull off any badly affected leaves as it regrows. If you do prune it back hard, keep it well fed and watered to help it resist infection.

If though, the infection is widespread and the shrub is looking generally poorly, it may not be healthy enough to respond to the hard pruning treatment. You can try spraying with fungicide (Scotts fungus clear ultra) though you may find it fairly ineffectual. There isn't really any treatment otherwise, so if it looks really bad, its probably best to remove it and choose another variety of plant instead.

Thanks Bamboo, I must say most of the shrubs there are 8 of them in a row forming a hedge don't look too bad. ie most of each shrub is in a healthy condition, although each shrub has a few infected leaves. It would break my heart to lose them, but me being a complete amateur I don't know what to do for the best, they attract an abundance of bees and butterflies in the late Spring/early Summer.

Yea, it is a pain, its a new infection in the last few years, and many fungicides which might have worked were so bad for the environment they've been withdrawn. I imagine, eventually, Escallonia will become as rare as hen's teeth. If its hedging, you probably don't want to cut it all back really hard either.

As for replacement, you might consider Berberis darwinii - it is prickly, but not a thorny beast like Pyracantha. Otherwise, Cotoneaster - most are semi evergreen, meaning they may lose leaves in cold winters, but they do at least flower and then have berries.The flowers are much loved by bees too. Ones to consider are C. lacteus and C. franchetii which gets larger.

Thanks Bamboo.

You could try giving it a balanced feed this spring and may be a mulch..... see if it helps it fight back.

I grew a hedge of Escallonia 'Iveyi' but I must admit it wasn't very successful. It had bare lower stems, leaf spot, yellowing of the leaves and this particular variety had lots of white flowers which attracted lots of bees but it held on to the dead flowers which needed to be removed by hand. Needless to say after about five years, I dug it up and replaced it with Taxus (Yew), which has been a winner.

Thanks Jimmy.