Vinca major in most places is very invasive.I guess they're struggling a bit under leylandi which sucks the water and nutrient out of the soil.

It spreads by runners and by pieces that lean down and touch the ground putting out roots.

If you want to encourage this just pin a few stems down to the ground with a stone or metal peg... they'll soon root.

In good soil vinca mahor will spread at an alarming rate.

This can be controlled by cutting them almost to the ground after flowering and they'll regrow and flower again in a few weeks.

If they are really struggling why not dig out a small hole where you want to peg the shoots down and fill it with good compost perhaps with a few gel crystals in it.

The term invasive applied to Vinca interprets as 'it gets everywhere'. As Anchorman says, it puts out long, lax growths which root at their tips - what you end up with is areas of bare ground with vinca plants popping up feet away, where those runners have touched the soil. As ground cover, I consider it utterly useless, frankly. If this bank you now have isn't compromised by leylandii close by, and it gets any sun, have a look at other plants for ground cover on it which cover the ground better and have different flowers - Iberis sempervirens, Saponaria ocymoides, Campanula portenschlagiana, Oreganum aureum, Helianthemums. All the ones mentioned are evergreen.

I agree entirely with Bamboos analysis. Vinca major is a lousy and untidy ground cover. The areas of bare ground between plants are a magnet for weeds.. Virtually any other evergreen ground spreading perennial or small shrub would make better ground cover. Pick something with "tight" foliage which will exclude almost all weeds

I wouldn't let vinca get within 10 miles of my garden ever again - it has made life incredibly difficult and frustrating for us for the past 6 years and is almost impossible to get rid of, smothering almost everything else planted in our rockery and spreading into the lawn.

What about Vinca Minor?

Thanks for your replies.

Maybe i'll have a rethink about ground cover for my 'bank' of earth, so any suggestions on a quick growing ground cover is much appreciated. The denser the better really as i don't really want alot of weeding etc in this part of the garden, its difficult to describe but this area is to the side of my property and only really seen by us when we park in that part of the driveway.

The bank is South west facing.

As for the Vinca Major underneath the leylandi in the rear garden just sounds like i need to train (pin it down) it a little better to provide some better coverage and maybe treat it to some compost to encourage growth.

Recommended treatment for Vinca is to lift up all the long growths and snip them back at about 6 inches - to be done in Spring. Makes a bushier plant less likely to sprawl a long distance with nasty gaps between.
Merlinbabydc: Vinca minor has shorter growths, but has the same problem, growing similarly.
South west facing will be fine for all the plants I've already mentioned, Ashb - all are reasonably quick growing, and all can be bought in small pots at the garden centre in early spring. Bear in mind that even just one Helianthemum (rock rose) will spread to about 18 inches all round... possibly in one season, but more likely after 2.