When navigating to the Apple UK website and viewing the iPad, to see that 4G is advertised just as it is in America, one may be tricked into believing that the iPad may at some point function in 4G on UK networks.
Faced with the potential embarrassment of being duped by Apple, it seems only appropriate to select the option 'Learn more about iPad with Wi-Fi + 4G', in the hopes of finding compatibility information on the next page. Instead, what can be found is a list of UK carriers offering data services, however, at the very bottom of the page in very small text is the message "4G coverage is not available in all areas and varies by carrier. See your carrier for details."
In fact, despite where and where not 4G coverage is available in the UK, or in fact, most of Europe, the current iPad will never function in 4G. In America and Canada, 4G runs on the 700Mhz and 2,100MHz spectrums, the only two supported by the iPad. In Germany, for example, with the only fully functional 4G network in Europe, the spectrums 800MHz, 1,800MHz and 2,600MHz are used. Likewise, current UK trials are for the 1,800MHz spectrum, with future bids covering the same range as Germany.
With the information confirmed by UK and European carriers, when perusing iPad marketing material, please just imagine that Apple meant to say three where it said four.