Fixing area at end of back garden - advice please

Since you have some hawthorn trees along the wall, why not leave them? They can be cut ruthlessly to create a preferred shape, they can be allowed to grow into trees if you prefer, or cut into bushes, they look nice and are virtually unkillable. Very bird and insect friendly.

You can still have a raised bed, just leave the area immediately around the hawthorns a bit low, eventually they will accept the higher soil level.

Lawn or gravel in the space is up to you, it sounds as though gravel may be better. If you have small children it will get everywhere, they can't resist it. In a north facing garden a lawn depends on how much light there is. Certainly put a membrane under gravel, it is one of the more useful purposes for membrane, but not in beds. Some weeds will grow anyway in the gravel above the membrane, but easy to pull out.

Its a good idea to put more soil down around the leylandii as the old soil will not be much good and there will be a lot of roots - they will eventually rot away. You don't have to completely cover them though, just plant round the stumps or put pots or whatever on them until they eventually rot away. They can look quite nice with a creeper - honeysuckle maybe - growing over them.

My personal choice would be gravel. Its going to have to be topped up every year or two anyway, certainly in the first couple of years, so it would work out cheaper. Also, its just my opinion and I know it would not be shared by everyone, but I don't like most of the decorative stone, its artificial looking to me.

The hawthorns against the wall; its hard to say without seeing the situation and the condition of the wall. On the whole I would doubt they would harm it, if they haven't by now it seems likely that they will not, but I can't say for sure. There is likely to be a mat of leylandii detritus which might be a good idea to remove and replace with soil, but I haven't had any immediate experience of them so I will defer to people who know. Could you put up a photo of the area?

Have a similar raised bank at the back of ours with a mix of large shrubs , holly , Pittosporum some black elder for flowers and photinia . Anything is better than the Leylandii . It is colourful and the birds love it . It is high enough as growing a long time but we cut it back and shape it every year

That and some topsoil or compost and a bit of weeding is about the size of the work to keep it nice .

In front of these we have medium to low size flowering perennials planted bit by bit interspersed with smaller flowering herbaceous plants which I change up every few years.

The stumps will rot down if you keep the muck and greenery topped up around it . May be a little acidic for a while with leylandii bits but most stuff mentioned will do well in whatever topsoil .

I would go with either a membrane and/ or a good well flattened area of aggregate checking the levels to make sure you don't get ponding . This can happen even with gravel .

Ask the landscaper to do this well ..that's his job and if you don't do this right you will get weeds and puddles and it will be a mess.

Like the idea of a nice grassy area up to the raised border . Is this the bit that gets the most sun ? If so it can get hard and compacted in summer ( if we get a summer !) so maybe the gravel or a few flagstones there long-term .

My two cents; rather than creating a straight 2m deep bed and a 2m strip of gravel I would lay sleepers at 45° to the wall in a zigzag creating a bed depth of between 1 and 4m. Then lay gravel in the angles with one larger area, 3m x3m, for a sitting area.

This gives more of an impression of being amongst the planting, breaks up the straight lines of the garden, and allows the planting of a tree or two in the deeper beds away from the wall.