Two temples in the UK. London Temple and Preston Temple (which also has an MTC and chapel on site). I had a relative that worked at the MTC.
There's also church office buildings. That's why GAs such as Jeffrey R Holland used to live here. However, they relocated recently to Frankfurt in Germany I believe, so they've not got so many employees in the UK anymore. They used to have houses for the GAs that worked here, but they probably sold them now that they're not needed.
There's also some church history landmarks here. I'm not sure if they're actually owned by the church, but they put on tours of them. One of the guys that did tours of them I'm 99% sure had his second anointing, and he ended up on the Preston Temple presidency recently.
Of course. It's all there on the lds.org website. All assets everywhere in the world, property deeds, corporate forms, executive compensation...everything.
Not to mention all documents from the Church Historian's Office, all minutes of First Presidency meetings, memos, letters...all there out in the open. The Church has nothing to hide from anyone, ever.