What would you like them to say?

You might look at Ilex crenata. This is a tiny leaved spineless holly that is fastigiate, ie it grows tall and thin like a poplar. It grows very slowly so would be OK in a large container for quite a long time. You could put bedding begonia sempervirens round it in summer before it gets too big and woodland type bulbs such as snowdrops or miniature daffodils for spring.

Depending on the size of the holly and the size of the container it might be wise to plant it in a smaller pot to start with, and sink that into the large one. Then plant the other plants round the outside of that pot.

Or you might try a Christmas Box -not very interesting most of the year but has fairly inconspicuous though very sweetly scented flowers in mi winter and is also evergreen..

Difficult for permanent planting - a couple of toparied box plants would make a statement, but won't like being in shade all the time and particularly won't like being exposed to cold winter winds, especially in the North of England. Otherwise you're stuck with tough but not exactly statement plants that don't mind total shade and cold temperatures, which is really only Sarcococca (Christmas Box), Prunus 'Otto Luyken', Skimmia fragrans, Liriope 'monroe white'. If it gets really cold (below zero day and night for a week) you should protect or insulate or move the pots so that the soil in them does not freeze. Hostas wouldn't do because they disappear in winter, so you'd be looking at empty pots for six months.

If you want to make a statement, its probably better to stick to temporary planting - small evergreens, ivy, pansies, and reckon on changing the planting again in late spring.

Bamboo, did you disagree with the Ilex suggestion? Its done well here but I haven't any experience of it further north. But it does make a statement.

Not necessarily; from your description, I'm guessing you mean Ilex crenata fastigiata, but they won't appreciate shade all year - they don't mind part shade, but on a north facing doorstep or close against the house, they're unlikely to get any sun at any point in the year. And unless they're well grown on in size, they won't make much of a 'statement', especially as they're slow growing.

That's true. Mine is a good four feet tall now but I've had it for a few years. Oh well, it was a nice idea while it lasted...

If they were bought as larger, more mature plants, and moved out into sunlight periodically, they'd be fine, Steragram, they don't need to be ruled out completely!

Several choices there then. I guess nobldy on here will be surprised to hear I would probably go for Euonymus fortunii variegata which does make a nice rounded clippable bush when it gets going and takes practically no upkeep....