skimmia are one of my favourite evergreen shrubs and they a pretty resilient.

Euonymus; Eleagnus ‘alata’; Viburnum ‘Onondaga ‘; Sorbaria Sem?

Euonymus fortunei varieties such as Emerald'n'Gold, Harlequin, Emerald n'Green, if he wants small, not E. japonicus... except Euonymus japonica 'Pierrolino' which is so slow growing it stays small for some years. Euonymus microphyllus as well, with its small leaves, looks almost like Hebe. Smaller Hebe varieties - H. youngii, Hebe odora, Hebe sutherlandii, Hebe pagei, H. 'Autumn Glory' (if you can find it) H. Green Globe, are all reliably hardy.
There are many new Hebe hybrids, but not all are entirely hardy...

And Yucca - specifically Yucca filamentosa 'Garland's Gold' or Yucca 'Golden Sword' - hardy as old boots, only get around 2 feet high, evergreen.

I have a Evergreen Viburnum tinus - Laurustinus in my south facing garden where I have heavy clay soil & I love it, it is evergreen doesn't need a lot of pruning, has nice flowers on it, I bought it because it is nice for flower arranging too LOL, he won't be disappointed with how it looks when clipped. That reminds me... I think I'll prune mine soon LOL.
Jackie x

Heavens no, do not plant Sorbaria Sem anywhere, it is the most appalling sucker producing thug going. Banned from planting in much of the USA as it is such a problem. I spend hours digging it out.
Some of the newer types of Daphne are good, slow growing, small and very fragrant.

Yes! I agree with Owdboggy about Sorbaria Sem....
Useful for waterside plantings but neglected plants can rapidly form thickets. :o((

A very sincere thank you for all your thoughtful suggestions. You have really considered our neighbour's situation and it is much appreciated.
We can now offer him help which is well-informed, thanks to each of you.
He is such a lovely man, brilliant at many things but NOT gardening! He wants us to be able to look out onto a prettier garden than he has at the moment!

Don't forget the option of planters or large tubs. Easy to grow nasturtiums & the like would zing nicely against dark slate

Darren, yes planters are a good idea and we could easily look after them with him ( or for him!)

My last front garden had a south-east facing aspect. I covered it with nice chippings (blue granite, very smart and fresh looking) and then I put a few pots on it with dwarf conifers (pinus etc) and planted a very few things into the soil. You don’t need a lot of plants for it to look smart. Evergreen grasses, rock-roses, lotus hirsutus, prostanthera cuneata. Evergreen is best, and choose things with flowers that look good against the gravel.

Karen, thanks for helping me with this. He won't need a lot as it is a fairly small plot. The blue granite chippings sound lovely and the idea of using evergreens makes a lot of sense too.

There is one drawback with keeping the plants in pots - the need to water regularly, even when its raining, when the plants are big enough to cover the soil in the pot.

True.