Nice to see a question with lots of information for once, but I do have two more queries - which way does the area face, North, South? And what part of the UK are you in (for climate reasons)?

if the walls facing theright way a climber each side of the window would look lovley or maybe some low ground covering conifers . you will have to dress the soil and add some nice healthy compost to the soil with all that cement either side and make sure you dont go above the damp cause as you will get mould indoors if you do . perhaps 2 identical planters and something identical in each like box hedging in them and haveawindow basket along under the window strangley enough lol . just a thaught .

I was going to suggest planters too, then they could change with the seasons :)

To Noseypotter
Thanks for the ideas, I like the idea of climbers but need help on the right ones. I already have plans for a Box hedge along two sides and I think window boxes and me are not made for each other. What low conifers were you thinking of?

To Bamboo
Thanks for your interest. I live in East Kent and the front of the house faces approximately east so gets good sun during late morning onwards. The soil is quite heavy clay.

Thanks again to both of you and I look forward to any other ideas you may like to pass on.

Sarcoccoca hookerania 'digyna' (evergreen, scented white flowers in winter); Euonymus fortunei varieties such as 'Emerald'n Gold' or Emerald Gaiety (both variegated evergreens, low growing); Viburnum davidii (large leaved, low growing evergreen); Hebe varieties such as H. Autumn Glory, H. albicans (but be careful, a lot of the Hebes aren't fully hardy, though the two I mention are); hardy Fuchsia (though these disappear in the winter) varieties such as Madame Cornelissen, Margaret Hunt; Berberis atropurpureum 'nana', Berberis 'Admiration', Berberis 'Bagatelle' (all deciduous); Spiraea 'Goldflame', deciduous, yellow leaves. All these are mostly below 4 feet, none over 5 feet tall to fit below that window.
Whatever you choose, make sure you plant at least 18 inches away from the base of the wall to allow the plants to bush out at the back as well as the front, and to expose them more to any rain that falls.

Thank you one and all. A special thank you to Bamboo for the suggestions. I will now research the suggested plants online and decide what to try - please wish me luck as I am no greenfingers.

your more than welcome x .

To "Bamboo"
Sorry for belated addition to my original question. I had a senior moment when I said that the front garden faces east - I meant WEST. Does this alter your recommendations?
Thanks in advance

No, it doesn't especially, though you could include Camellia now if you wanted a larger shrub, lol!

Thank you Bamboo.

I meant to say that I got your PM, but also a notification that something had been added to your original question, so I'd have seen it anyway.