Will the 4G LTE used in an iPad bought in England also work in Sweden?
No.
The LTE standard uses different frequencies in the US and Europe. However, the model sold in Europe is the US model. This has been officially confirmed by Apple [1, german].
LTE in the iPad
The iPad supports only the frequencies 700 and 2100 MHz [2] for LTE use. These frequencies are not used for LTE in the EU.
If you take a look at the footnotes, Apple states on their website (US and foreign) that:
4G LTE (is only) supported on AT&T and Verizon networks in the U.S.; Bell, Rogers, and Telus networks in Canada.
LTE worldwide [3]
The following frequencies aren't really such even numbers. They are frequency bands that spread out over a whole spectrum of which little fragments are divided among carriers.
- USA: 700, 1800, 2100 MHz
- Canada and Mexico: 1800, 2100 MHz
- European Union: 800, 1800, 2600 MHz * (bands in use differ widely)
- Asia in general: 1800, 2600 MHz
- Australia: 1800 MHz
There also exists this table [4] which lists very detailed information on frequencies bands used world wide. You can see here that the the 2100 MHz band is used for UMTS and IMT (= 3G standards) in Europe. The 700 MHz band does not seem to be used by carries in Europe.
Here's an article that specifically mentions that the new iPad will not support 4G connectivity in Sweden:
While there has been a rapid build-out of 4G networks in the U.S. and countries such as South Korea, LTE is still scarce in Europe. Even in Sweden, one of the few European countries with broad LTE coverage, it seems users of the new iPad won’t be able to make use of the 4G connectivity.
Swedish telecom newsletter Telekomnyheterna noted that the new iPad only supports LTE on the 700 MHz and 2100 MHz frequencies. In Sweden the 700 MHz frequency band is used for television broadcasts, while the 2100 band is used for 3G data traffic, and it’s unlikely that any of these bands will be re-farmed to LTE.
Source: http://blogs.wsj.com/tech-europe/2012/03/08/new-ipad-not-quite-so-fast-in-europe/
(The article does leave open the possibility that Apple may still release a different configuration of the new iPad supporting 4G connectivity in Europe.)
Sadly the term "4G" has been co-opted by marketing, and it's hard to know what anyone means when they use it.
Gizmodo reports that here in the UK, as in the US, each carrier has a different 4G standard, and the iPad 3 as sold here may not work with "4G" on any British carriers. Apple have crammed a huge number of radio protocols into that thing, though, so even if it can't get 4G speeds it can get "3G+" on networks like Three.
The practical answer is that an iPad 3 that you buy in the UK will definitely work on the Swedish mobile networks, and that you're likely to see better speeds that you would with an iPad 2. As @Rinzwind points out you will definitely not get 4G in Sweden with a British iPad, but you won't really be getting 4G in the UK either.