Hassles will be your biggest enemy. The power cord will handle the different voltages/amp requirements, BUT the plug prongs, as I'm sure you're aware, will not fit in British electrical sockets. I am not certain, but I believe the plug portion of power cord can be popped off and replaced by a British plug head (I did this with my old iPod touch charger when I went to Europe. I purchased the European plug head off eBay, then just swapped them, once I got to Frankfurt. I assume you can find plug attachments for the British variant on eBay also). OR you can charge the device with an existing iPhone/iPod charger OR through the USB port on your computer, BUT this will take significantly longer than the native charger provided (the provided charger is indeed 10V, while the iPod charger is 5v I believe). You also cannot! use the device while it's charging and the screen should be off, this will allow the device to charge faster. So that of course is hassle number one, but if you have an iPod/iPhone charger it's not a huge deal unless you want fast charging.
Problem two would be the 3G issue, should you opt to purchase the 3G version of the iPad. The sim card is ejectable and the ejection tool is provided, if not a safety pin can be used. The device will come with an AT&T micro-sim card preinstalled, which you'll have to remove. You'll then have to wait until mobile carrier services in the UK begin offering iPad specific data plans, then go through the process of acquiring the service and micro-sim card. This will mostly likely be in the end of May.
Another issue will be availability of iPad specific apps in the UK iTunes store. Until the iPad is officially released in the UK, the UK iTunes store will only carry iPhone/iPod apps that I've been updated to include an iPad version buoy into the the iPhone/iPod version. you also will not be able to search for iPad specific apps until late May.
The keyboard isn't an issue, it's on screen and like all iPods/iPhones/iPads, can be changed to reflect region specific differences in the personal settings menus.
Hope this helps