Pretty much any charger with a micro-usb connector will work. Does the UK version come with a microusb cable? you can use that to plug into any usb port and charge that way, unless your workplace prohibits that (mine does). I use a spare blackberry charger (5V 700mA) at work for mine, seems to work well.

http://www.amazon.co.uk/s/ref=sr_nr_n_1?rh=n%3A329082031%2Ck%3Amicrousb+charger&keywords=microusb+charger&ie=UTF8&qid=1387385541&rnid=1642204031

This link shows quite a few candidates, at various prices. I try to stick with items sold by Amazon directly.

 

I don't have a recommendation, but the included charger is rated at 1.2A, while most phone chargers are rated at less than 1A. A charger rated at 1.2A or higher should charge the phone just as fast as the included charger. Just make sure the output on the charger is 5.0V. I've seen some generic chargers that output 5.7V, and they've caused problems with phones I've plugged into them.