Basically a shrunken down, mid-level Xperia Z
Update: A Sony Mobile spokesperson tells Android Central that the company has "nothing to announce" at this stage with regards to UK availability for the Xperia ZR.
Original story: Sony has expanded its Xperia Z family today with the new, 4.55-inch Xperia ZR. Packing many of the same internal components -- and Xperia Z-like waterproof capabilities, (rated IP55 and IP58) the ZR will represent Sony in the mid to high-end space. In fact, Sony's touting its higher IP rating (the Xperia Z is rated IP55 and IP57) as making the ZR ideal for underwater HD video recording, if that's your thing.
Under the hood it's running a 1.5GHz quad-core CPU -- the same Qualcomm Snapdragon S4 Pro that's powering Xperias Z and ZL -- with 2GB of RAM, 8GB of internal storage and a microSD slot. On the front there's a 4.55-inch 720p display (in places described as a 4.6-inch panel, so go figure), and around the back is a 13-megapixel Sony Exmor RS camera with LED flash. All in all, a respectable set of components, and the ZR's curved back should make it a good deal more comfortable to hold than its brick-like sibling.
Sony's press release says the Xperia ZR includes LTE support, but the official spec sheet only mentions HSPA+, so it's possible this may depend on which market you're in. As far as HSPA+ connectivity is concerned, it seems there'll be one version supporting 900 and 2100MHz (for Europe) and another with 850, 1700, 1900 and 2100MHz support, likely for North America.
The Xperia ZR will land in "various global markets" during Q2, so make of that what you will.
Source: Sony Mobile, Press Release (PDF)