Try London Plane although the leaves don't look to have the shape.

I thought possibly a lime tree/ Tilia species by the leaf but the fruits look wrong.

Online pics of leaves/fruit/bark of the Large Leaved Lime (Tilia platyphyllos) seem to match?

Do the fruits have a long thin leaf like structure next to them? I cant see them in the picture which is why I queried lime. I agree leaves and form and bark suggest it.

The foliage looks like an Osage Orange, but the fruit isn't right for that. Maybe a different member of the Moraceae?

(On my PC) I can see the thin leaf-like structures above the fruits on the left.
More structures are also above the fruits next to them (higher up, just to the right of the previous ones), but are half hidden behind a regular leaf.

Thank you everyone. Sorry I haven't responded...been away for a couple of days. I think a Large Leafed Lime would be correct, but the next time I'm in the park, if there's one of the gardeners around I'll ask if they know.

Yep, it's a Lime tree. The bracts above the fruit look like they are shaped more like those from Tilia cordata.

You're spot on Tug' according to one of the gardeners. He was also impressed I even spotted it as a Lime...I had to confess to having a little help :-))