Looks like a type of Sorbus - Ash or Rowan.

They have the most beautiful bright lime green leaves. Thanks Kildermorie.

The parent plant could be quite far away and may have been seeded by birds carrying the seeds off, especially the Rowan, that has orange berries. The seeds of the Ash tree has winged shaped seeds instead of berries.

Hope this helps Nancy?... Myron

Thanks Myron, I imagine that they will be chopped down by the maintenance team unless a few manage to escape, I will keep an eye on them.

What with ash die back, it seems a shame to just eliminate them.

I'm sure this one will go as it's in the middle of the grass verge but there are quite a few in the hedgerow so hopefully they will be spared .

Are we completely certain that it is a Sorbus? I am not sure. Whilst it has similar characteristics it does not look quite right for a Sorbus seedling - far too many twiggy branchlets down to the ground and too many leaflets per leaf ( and it could still be a species that I am not familiar with)
As an alternative, anyone any thoughts on Mimosa? This can be an invasive 'weed' but I have no idea if it would occurr in Oxfordshire.

I doubt Mimosa as the leaves are too big Bulba. It could be pseudoacacia which is far hardier and a European native but it does remind me of an Ash seedling. I think it looks twiggy as it is struggling to grow out of the hedge, hit sun and then grew like mad. Some of my Rowan saplings went from 30cm to 2 metres this summer!

Leaf pattern (the way it's set on the stem) tells me it's a robinia. If they were all fairly close to each other, I would have said possibly suckers off an old rootstock.

If they are Robinias, they will develop thorns where the leaves join the stem.

I am beginning to think Robina Pseudoacacia as well as it does have the right colour and shape.

I think you could be right Hortum and Kildermorie, I just looked up Robina Pseudoacacia and the pic is the same as a tree that was removed about a year or so ago 6 yards away from where these seedlings are appearing. Thanks you all for your input.

Got there in the end Nanjo!

Sure did Kildermorie :-)

They may not even be seedlings, Nanjo--Robinias are notorious for sending up shoots from the roots. You may need to apply some SBK to get rid of them.

Thanks Tug but not a problem as they are quite a distance from where I live on the estate.