Metres or feet? It's just I can see what looks like a flowerpot to the left bottom of the pic, which would mean your shrub is not more than 3 feet high... Also, it was either windy when you took it, or its out of focus - can't see it clearly.

3m is the height of a tall man with a child standing on his shoulders. 1.8 metres is about the height of a small to average woman. I have never heard of a hebe growing to that size (although if you google them you will find a lot of different estimates of eventual height) and I think you must mean feet not metres. At all events you can clip them or even cut them back if you need to, so don't worry. This type of shrub shouldn't really need much if any routine pruning though as it is a nice compact shape and very well behaved.

I will add another photo tomorrow in daylight. No I did mean metres! I have since looked again and would say that it is about 3 metres square. All the photos that I have checked against hebes suggest that it is the same plant but it still seems a bit of a mystery, particularly because of it's size.
So, anymore suggestions would be gratefuly recieved!

By the way, the flower pot in the photo is actually a builders bucket :) !

That would make it 10 feet by 10 feet, roughly - I'll be interested to see a clearer shot to determine exactly what it is, if possible.

The photo is so out of focus it is difficult to tell but I don't think that is a hebe.

Please see new photos added in a new question. Many thanks for responding.