With the best will in the world the trees are yours to keep or remove.
Why not have a chat with your neighbours and tell them you'll replant with more interesting and wildlife friendly trees?
You seem to have a lot of other large shrubs to maintain privacy - it isn't as though you're proposing to remove everything.

Why not try Sorbus, Betula, Gleditsia and Crataegus and maybe Ilex.

Just get those conifers out. Good luck!

Yes it's your choice, not theirs, but conifers do tend to take over, have a shallow root system and could be replaced with some nice shrubs or trees.

Thanks guys. I agree that those monsters have to go!! Once its done I will post pictures of before and after planting. Thanks for the tree suggestions - I will have a think.

Beech (or hornbeam for heavy soils) can be used. When treated as a hedge, they hold on to their dead leaves all winter, so you have a barrier for twelve months of the year, but they can be cut back annually in August

If it is a Cypress then there may be an option to top it. You are right that that may not be a pretty sight but some Cypress can be used as a hedge and regrow - unlike Pines etc.

If not then Andrew's suggestion of Hornbeam or Beech will work. Bare root plants should be available now.

We are about to have our back and side boundary trees downsized. A long time ago we planted Hawthorn, amazingly bird friendly tree, they love it. Laburnum an upright form but it is now very tall. A Rowan lots of lovely berries for the birds. Four Camellias facing north and all doing well. Don't plant Hazel ,as we did, or you will have them all over your garden once squirrels find it with nuts forming. We removed umpteen large tall conifers before this planting. Maybe choose tall shrubs. We have a huge Mahonia on our boundary giving a marvellous perfumed display of of sprays of yellow flowers, a joy at this time of the year and late forage for bees too, berries for birds later.

Escallonia is evergreen, fast growing in the early years and can be cut to keep it to the desired size and shape. It will flower all summer. There are versions with Red, pink and white flowers.

If you want fast growing choose Eucalyptus varieties - but, they do get over 50 feet fairly quickly, and some varieties (E. gunii included) drop scrolls of bark everywhere.

I think if she planted Eucalyptus she would need to cut it back severely to make it into a thick bush rather than a very tall tree which is what she is trying to get away from with the cupressis. Low down it is not a very good tree from the privacy point of view.

I was thinking of panting a native hedge row and mixing it up a little.Hawthorn, blackthorn sloe, field maple, wild privit, field & guelder rose ? That way I will have a variety of colour, foliage and it would be good for wildlife. Trouble is it would have to be planted against or close to wooden fence panels which are 6ft high. Any thoughts? Many thanks & your thoughts and suggestions are hugely appreciated as I am only gardener in the family and am not always sure myself!

I must have misunderstood what you meant by 'semi mature TREES', since you're actually wanting a hedge, sorry.

A 6' high fence with a 2' trellis on top with Clematis honeysuckle, pyracantha etc trained on wires or maybe fruit trees espaliered along it would be my own preference. In front have a mixed border of low growing evergreen shrubs and herbaceous perennials. Hedges planted next to a fence will either push it over or cause it to rot eventually.

I would ask next door if they want it kept , if they would like to pay as in a couple of years you will be doing the same thing , its just happened by me £2,000 to take the tops out from a conifer hedge that had never been pruned in 20 years all bare at the base and just no sunshine in the gardens , that was 6 years ago and they need doing again

Take it out , thats what I would do , you have lots of other lovely shrubs already so it isnt going to look that bare

I agree with Gnarly gnon, the same thing happened next door to me at the bottom of there garden, the tops were cut down and they just grew back again and now they are as bad as ever, best thing is get rid and plant with some other hedging if you need to, it is your garden not your neighbours.

Yes you are right. Will post picture of area once trees have been taken down which will be done in a months time.

I'll be interested to see what you do. I like the native hedge idea.