Could anyone recommend a tree for me?

What do you mean by "standards", Looby? In gardening, a standard is a shrub trained into a miniature "lollipop tree" shape. Nowadays in the States, they are more often called "patio trees".

I mean traditional tree shaped. Lollipop shape if you like.
Thanks

So, single trunks, more or less round heads, low maintenance, and with evergreen leaves. Hmmm. It's going to be hard, since most of the evergreen trees in the UK are going to be conifers, which tend toward the "Christmas Tree" shape, or are happier with multiple trunks. Some of the larger varieties of Holly are a possibility, though many also prefer to have multiple trunks. In the milder parts of the UK, you can add such semi-hardy trees as Southern Magnolia, Holm Oak--eventually too big, but slow growing--or English Laurel, which can be trained to a tree shape where frost damage is rare. There are probably others, but locals would know them better than I would.

I had thought about Hollies but wasn't sure which type is the best shape. What would you advise?
On the south facing border if I was to go for conifers what would you recommend that was maintenance free and not too tall 15' max. Probably need 3 or 4, which I'd like to make a feature.
Thanks for replying by the way. :)

Probably some of the narrow Junipers, such as 'Robusta Green', or 'Blue Point'. Some Oriental Arborvitaes (Platycladus orientalis) could work, too. Unfortunately, none of these make good trunks. I'm not certain about the Hollies, since I am more familiar with the ones that grow here, of course! I would ask about the local garden centers and anyone you know is a local plant freak, Looby. I'm pretty sure that any of the varieties of English Holly (Ilex aquifolium) would be hardy, but I'm not sure which ones would be easier to train into a tree, though I would look at the ones that grew large first.

Thanks for your reply it's very helpful. I think a variety of conifers along the border will look good and I have Googled the images of the ones you have suggested. I think thats the route I will take.
Thank you again for your help I really appreciate it.

You're welcome!