I'm confused - if your garden is west facing, then it shouldn't be in sun until the afternoon rather than from 10 am in the morning. Secondly, I'm wondering why you want a tall evergreen in that square bed, because it'll block your view of the lower planting area. However, plants to consider would be Carpenteria californica 'Ladham's Variety' (assuming it really does get sun most of the day), Photina 'Red Robin', Viburnum tinus. You'll need something to cover the ground, particularly at the four corners, so accompanying shrubs which are evergreen could be lavender, santolina, senecio. Or for even lower evergreen ground cover which flowers, Helianthemums, Iberis.
If you wanted another bamboo, use a rhizome root barrier - these are available online by length, and should be inserted vertically into the soil at a depth of 18 inches, all round the part where you want the bamboo to grow to contain its root spread.
Personally, though, I'd choose planting which didn't get higher than about 4 or 5 feet, such as Phormium, and reserve the taller evergreens for the area further back.

Hi Bamboo and many thanks for your response. We get the sun quite early in the back garden but it may be a bit later than 10 especially in the winter months - so perhaps we are not fully west facing after all.

The reason we want something that grows high is to provide screening/privacy for our seating area (to the right of the square) as our house sits between two roads with peoples gardens backing onto ours and because one road is higher than the other when I'm standing by the square and look to my left I can virtually see into those people's gardens and I'm sure they dont want to see me and I don't want to see them!

I have just bought 4 x 5ft Photinia Red Robins to provide screening on the left side and so thought it would be better to have something different in the centre. I will take a look at the plants you have mentioned as it may be that one of these will look good here. We had a Phormium in the garden pre-landscaping and I did think about getting another one but was slightly put off because I didn't think it would grow quick and high enough. I think the red/bronze coloured phormiums look lovely. I will also take a look on the net for the root barrier for bamboos as that would be my ideal choice for this space as they add colour, screening and interest all year around.

I see - I thought there might be a reason, but didn't know what it would be - privacy's a good one! If you can bear to do the work of inserting a rhizome barrier, I reckon bamboo would be the best option - it grows faster than any of the shrubs mentioned for one thing, and you can buy pretty big specimens to start with.
As for the sun, sounds as if you're south/south west facing.

Thanks Bamboo. I've found some sites selling rhizome barriers and am sure that my builder would put one in for me.

Bamboos are lovely plants its just a shame that they do tend to spread. I understand that even the non-invasive ones tend to spread a bit these days so a barrier would help contain a non-invasive one as well.

I may need to twist my hubby's arm though re putting one in the new garden given the problems that we had with the previous one but I'm sure I can work on him!

Thanks again and enjoy the rest of your weekend.

Would you consider a nice fruit tree or maybe a magnolia, neither fast growing I'm afraid but give all year round interest, you could plant box balls in each corner or even a box hedge all round the square, also consider an Acer, grown for its colour, but delicate.
How about,

Betula 'Jacquemontii' (White Stem Birch Tree) , take a look on www.mailordertrees.co.uk for more ideas and good prices.

Nice ideas Grandmage, but they wouldn't give privacy at table height.
Littlet - you're right, even the so called clump forming non running ones tend to run now in this country, so a rhizome barrier has to be considered essential. Just make sure you builder inserts it correctly down to the right depth though...

Possibly go with phllostachys Aurea[ the golden bamboo] this one is ideal in large planters and ideal in the ground, and is a clumper, i find these very easy to grow in the ground and dont seem to have any problems with them running, the secret is to divide the clump every so often which will give you more plants, i find these to be quite slow at forming largish clumps, now in that situation you have there why not plant some lavender dont directly underplant but come in a little from each corner, the combination is fantastic, keep these trimmed properly over the years to prevent them getting leggy/woody, equally good is to surround the plant with rosemarry and apply the same pruining like lavender, both these suggestions i have used to good effect, dont forget the waffting scent of lavender through the summer will be such a joy.

You could use a willow screen, (with clematis, jasmin, honeysuckle, growing up it,) to the height that you require and then have something special growing in the square behind it! (lavendar, great for our bees) Such a shame to just fill the square with Bamboo when there are other delighful plants that you an use.

Julien's suggestion of Phyllostachys I'd go with, though I prefer P. nigra. However, I still would put a barrier in place - I planted this 5 years ago in a bed within paving, understanding that it didn't run. What nonsense, not only has it run, its under the blasted paving and popping up 8 feet away. I really, really regret not putting a strong enough barrier in place. I'm in the South, and as you're in Essex, you'll likely have the same trouble.

I was thinking of a Yew tree. You can shape them, they take little care, location is good, evergreen and diffuse wind and provide privacy. They are slow growing at first but once settled they grow quicker than you think. You can buy them bare root at this time of year quite reasonably. The other thing I was thinking was a Holly standards but it will take years before it provides a screen.

The 2 goldcrest wilma conifers I see in the pots will be 12ft in a few years if you put them in the ground.

Pittosporum tenuiflorum ... very eye catching small evergreen variegated leafed tree with contrasting dark bark. Helen Yemm of Daily Telegraph recommends it - see her blog under plant name on google. It can be easily pruned to size so will never get too large. It doesn't like an unprotected open field spot in hard frosts or cold winds, but your garden looks perfect for it.

I use the biggest black nylon pots for my bamboo with the bottom cut out . as the buckets slope outwards and out any new rizomes come out the top . i bury them so the bamboo can't split the pot . this way you can have more varieties in the same bed . You ofcourse could get clump formers to . also smaller grasses and have a theme . just a thaught .

Had you thought of using trellis by the fence instead as I see your neighbour has done? Then you could have a pretty climber on it and something lower in the square bed.

I always like something a bit lower in the spare bed steragram lol sorry couldn't help myself x x you got to have a laugh .

Many thanks for all of your comments and suggestions and it has certainly given me something to think about. My hubby is still not overly keen on the bamboo idea but I will look into the varieties that have been mentioned. Trees aren’t really my thing and I don’t want to have lots of leaves to clear up as I’m looking for a maintenance free type garden if I can.

I’m planning on putting a climber or two on the trellis at the back and am thinking of a clematis and also climbing rose (we used to have an Iceberg which did well in that area but I would like something red or peachy coloured this time around). I also want few lavender bushes either around the edge of the square or in some of other borders.

The funny shaped border at the front of the garden will be my veggie patch although I’m not sure what I will grow there yet. I grew green beans, beetroot, carrots, courgettes and salad leaves all in pots last year so may go for more of the same but will grow the carrots in pots.

Anyway I must say what a lovely forum this is and it’s nice and I look forward to using it throughout the year.

If you don't want leaves to clear up, you won't escape that with bamboo - it drops leaves all the time once its mature. The bed where I grow it is constantly full of dead leaves, which are light enough to blow all over the garden and more difficult to collect, I'd say, than tree leaves, which at least all come down at once. That's the trouble with evergreens - they drop leaves year round in a sort of steady supply rather than a glut in the autumn, lol! Have a look under the nearest holly tree you can find - there'll be a layer of dead, prickly leaves beneath...
You could consider something deciduous instead (how about Amelanchier ballerina, for instance) because you won't, presumably, be sitting outside during winter when whatever it is has lost its leaves...

You could choose pyracantha, this is evergreen and gives plenty of interest through the year, lovely clusters of white flowers early summer followed by clusters of berries through the autumn/winter either orange,yellow or red, i would consider putting in a stake to keep it upright as they can rock about a bit once they get to six feet or so, i agree with bamboo regarding the leaf drop, but its only a small area you have for planting and would be litterally a two minuit job once a week, just to add pyracantha is a great choice but consider it has lots of sharpe spines so young kids would need to be aware, if you choose bamboo then they do like to be kept moist, lack of water results in the leaves curling, but dont worry once watered they perk up very quickly, also you get a lovely rustleing sound in the wind with bamboo, i stick a lantern next to mine and this gives a lovely effect next to the foliage.

Your more than welcome .