[rookie1]

Good evening
Just noticed today that our rowan tree is looking a bit ropey, with blotches on the leaves and many going brown. Never noticed this before and just wondering if it is something serious that we should be worried about? Any thoughts on what is affecting the tree and what might be done about it?
See pix attached.

[Yorkie]

I can't really tell from the photos, but a quick internet search suggests that some of the diseases that can affect rowan trees are:
Fire blight, a bacterial disease that attacks the rowan through its open wounds and causes dead branches and defoliation.
Crown gall, a bacterial disease that causes tumor-like growths on the roots and stems of the rowan.
Powdery mildew, a fungal disease that infects the rowan's foliage, stems and fruit with a white, powdery coating.
European mountain ash ringspot-associated virus, a viral disease that causes yellow spots and rings on the rowan's leaves and reduces its growth and fruiting.
Silver leaf disease, a fungal disease that causes the rowan's leaves to turn silver and die.

Might any of those be relevant?
Is the trunk showing any signs of unusual cracking, or weepage from it?

[Aunt Sally]

Is it not just autumn colours before the leaves fall?

[New shoot]

It does look like some sort of black spot disease on the leaves as well as the general colour change.  Rowans are part of the rosaceae family, which includes roses, and can get this.

I would clear up as many leaves as you can once they fall, but if it black spot, it is not necessarily a huge concern.  There are a lot of fungal plant diseases around this year due to the weather.  Mild and wet conditions are prime for spreading them.