Yes.....purely for the winter. Chuck them away come spring.
Cool wave is what she wanted.
Thanks
The best choice for trailing Pansy.
Ok, background plants. If you want height these are almost bound to be evergreen shrubs or conifers. Plants grow slowly in winter so you will need to buy something which has already achieved the height you want.
My first thought is grasses. Wide range of colour and form which could be left in the container in summer and contrast well with bedding plants. Grasses could also be happily dug out of the container and repositioned elsewhere, a lot of the other options won't like this.
Evergreens are generally slow growing and therefore more expensive. There are some which are grown in millions specifically for this purpose and they will be cheaper. There are a few conifers grown this way, for bright gold colour look for Cupressus macrocarpa Goldcrest or similar. There are a number of different varieties or cultivars, by variety/cultivar mean the last name. It's the first two which are more important. You'll find quite a range of blue or green conifers. The Goldcrest and similar will prefer protection from cold wind. It's almost certainly the one you will see in garden centres.
For evergreen shrubs consider Skimmia, winter flowering heather, taller Euonymous, perhaps "evergreen" Euphorbia.
By all means have a look through the shrub area for ideas but you are more likely to find these items in the area dedicated to bedding plant or looking good/impulse plants.
You will find better ranges in a decent garden centre than B&Q etc. but "might" strike lucky at Aldi.
Sorry to use botanical names, there either aren't any or I don't know them.