Junipers can only be pruned when they are young, and then only lightly, although you could trim it over very lightly. They do not grow from old wood, so if you cut it down, it will die.

Thanks Bamboo, back to the drawing board then.

Take it out and choose something that doesn't get so big. These usually outgrow their allotted space in smaller gardens, so their life in those is not long term.

From this pic, it looks more like a Juniperus squamata 'Blue Carpet' and they by their very nature can be cut back reasonably hard as long as plenty of newer growth is still left intact so that it can grow away again over a couple of years and cover over all the heavy pruning. It's a ground cover conifer and better able to handle such harsh treatment. note - the cultivar 'Meyeri' is an upright irregular growing Juniper.

Thank you for your advice Bluespruce, I shall try and follow your instructions and then if all fails and I make a mess of it I can replace it.

It's certainly worth a go, you'll be surprised how quickly this plant will grow out again given the time to re establish.