Privacy hedging

Not instant height, I'm afraid, but how about Rosa rugosa grown as a hedge? It can grow to about 2 metres tall, with fragrant flowers in summer followed by large hips in autumn, but it is deciduous, and will have a rather informal look.

It depends on the size of your garden but when a block of flats was built next door to us I realised they had a much better view of our once private garden than we do. I didn't like going outside. So we planted a willow bower to give ourselves privacy. It is very fast growing so before long we could sit inside, drinking our coffee or wine. Reading or knitting and look out away from the flats. It's rather old and tatty now but I still love it. I also grew roses up the sides so it smells fragrant too in the summer.
I am sure you and the designer will find a solution.

Please think about how it will impact on your neighbour.

The back of my house faces north and has another house on the east side and the neighbours have grown large trees all along the west fence with the result that my garden gets no sun at all in the summer.

I had to pay £300 to have all the overhanging branches lopped and taken away. It did seem unfair.

Thank you everyone for your help. Some food for thought there, we have a landscape gardener coming tomorrow to have a look.

A row of bamboos would be lovely and they move with the breeze. Looks good all year round and easy to thin out by harvesting a few canes. Just don't choose a very vigorous variety

Good idea FF, anything but a hedge. I have to trim my side of next door's 100 foot monstrosity, all along the top, every year. I'm not at all happy with balancing on ladders at my age!

Strong trellis on top of the wall with pyracantha growing up it for height with various colour berries which also attract the birds. Not instant height but very fast growing. Interplant with other climbers such as clematis for flowers, montana is very quick growing.

Not Leylandii, whatever you do! In fact, anything fast-growing that's in the ground rather than a container, is going to need frequent trimming and attention.

Have you considered a pergola with climbers? That would be my first choice. Bamboo and Pampas grass in containers are fairly low maintenance.

If you want trees then multi-stemmed Betula Jackmontii (birch) or Rowan, perhaps, but they'd only screen in the summer. Tall evergreens may block too much light. How about installing posts and a large, rectangular sail (sunshade)?

Maybe a combination of the above?