Screening

Have you seen the topic below this one about privet? http://www.hedginguk.com/privet.html is a site you can look at. Pyracantha is horribly spiny but would be good if you didn't mind that. What about Eleagnus or Photinia Red Robin? I have Eleagnus Gilt Edge which has gold around the leaves - good for bouquets at Christmas! It's grown pretty big, so has my Photinia.

I'd be wary of trying to blot out the monstrosity entirely. The only things that would do that would create their own problems. If there's something attractive in front of it your eye will be drawn to that. If you have a fence at the bottom I would go for small trees to screen the upper levels. That way you'd still be able to get along the back of the greenhouse. A lot of the crabs, cherries, sorbus, laburnums would do the job. 

As Busy-Lizzie says pyracantha is horribly spiny, it wouldn't be long before it spread forward to the greenhouse then you'd have a painful fight with it. 

"evergreen and tall, to get to around 15 ft min"

You are talking conifers then as 15ft would be a mature (10-15 year at least) climbing plant. Have a look at Cypress - these make good screens, grow thinly and can be cut back. they also grow tall quite quickly.

I have the same problem by the side of the house ,some one has built a extension that looks like a toilet block and I have to look at it.I am hoping to get him to  grow a clematis Montana up it ,one its quick and looks good and you can clip it into shape and I will have something nicer to look at but I suspect I will have to put some trellis up and do it my my self.

Bamboos make very good screening plants. You simply need to get a variety that exactly suits your requirements. You need to make sure you get one that is erect (that does not flop with rain or snow on the leaves), and does not have invasive spreading roots. Most bamboos are fast growing, and many are evergreen.

One that may be quite suitable for you is Semiarundinaria fastuosa. They are not cheap, but you can buy them already at 8 feet, and they will get to 15 feet within a couple of years, and taller.

That's not my garden, although I do have several of these plants.

There are hundreds of species of bamboo, and there may be other, even better, species. A specialist bamboo nursery could give you some good advice.

I think this is one for the planning authority.  If approaching the council doesn't work speak to your local councillor or even MP directly.

I agree with dovefromabove - take it as far as you can, make a nuisance of yourself, he shouldn't be allowed to get away with it- what will he do next??

Write a chronology of the incidents of nuisance and the council's response and send it with a covering letter to your local councillor and get your neighbours to do the same. At the same time send a copy to your MP.

Photographs might be a good idea too (whilst taking care not to invade your neighbour's privacy). 

Good luck.

You have my sympathies Carney!  We have a very similar problem with our neighbour behind us who is an absolute pain with noise from cars and from his garage!  Due to him cutting some trees down we were also left with no privacy from his side windows and we have gone for Cherry Laurel for fast growing dense screening.  Mine is currently growing in a similar sized gap between my fence and greenhouse but getting big very quickly so I fear greenhouse will have to go - privacy is more important to me and it won't be getting any sun/light soon! I have a pyracantha to add to my screen too but is growing nowhere near as fast as the laurel.  I also have a Solanum Crispum which has grown very quickly and is semi evergreen and is currently supported by a trellis on stilts next to the fence - might be another option?