If you are near the sea you could use the best hedge would be Euonymus japonicus, but others could be used such as Hebe franciscana, olearia, fuchsia or griselinia. These have suffered frost damage inland this winter but, being close to the sea, there is unlikely to be a problem. Holly is a good solid hedge for seaside use.
.I attach a photo of trees . planted 5 years ago that which were supposed to grow within 2 years to 6′ but have not grown. Please can you advise what I can do to encourage growth or should these be replaced. The site is exposed and near the sea. I require a shelter belt/ privicy hedge.
This looks like spiraea and there are small-growing forms of this. They do not make a good hedging plant in any case as they are too bushy.