What tree is this?

[Jux]

I'm sure it's nothing special. There are two which jave self-seeded in a part of the grden I can't get to easily so I honestly hadn't really seen them before. I don't know what they are nor how big they'll likely grow. They're rather close to the house but round a corner iyswim, where we'd allowed some other people to do a bit of gardening for a few years.

Forsythia?

It's a prunus. Maybe blackthorn

Yes, I think blackthorn too.

I agree it's probably a prunus. It reminds me of a cherry plum (I've two behind my garden) but hard to tell from the photo. This link gives some advice on telling them apart from blackthorn - earthstar.blog/2018/04/10/cherry-plum-or-blackthorn/

Not blackthorn because the leaves are out at the same time as the blossom. Therefore cherry plum, although late for cherry plum. Thorns would suggest blackthorn, as would a very dark colour of young twigs. The thing about the sepals being bent back in cherry plum isnt mentioned as a diagnostic difference in the authoritative field guides so perhaps isn’t universal. A Prunus species, anyway.

… has 4-petalled yellow flowers

The bees will love the blossom and you might get fruit if its a prunus. Blackthorn great for wildlife.

Yeah, sorry. I haven't got very good eyesight. It's too early for forsythia too, I expect. I agree it's more like a blackthorn.

Forsythia is in full flower round there (Yorkshire)

I meant here not there

A snowy mesiphilus perhaps, I'm looking out at one in my garden and it seems v similar.

No it's not that - I have one too. Agree with others that it is some sort of prunus.

Thank you all. I've looked up prunus and agree it's most likely that. I jave the words "ornamental cherry" going through my head.....