iPad 4 with Cellular (Which network?)

Actually it does not matter since the iPad is not locked to a carrier...but since your goal is the UK, go for the AT&T model since that is a GSM network also.

Ralph is spot on, but be sure to check around on these boards for people who have done the same.

There are loads of tickets from people who bought an iPad in the US to save some money and are now angry at Apple because something has gone wrong and the warranty is good only where they bought it.

You have been warned :-)

Alfred brings up a very good point, in the past the warranty for the iPad was universal, but with the expansion of models and WiFi/cellular models world-wide, the warranty is now country-specific. You cannot get service except in the country of sale. And Apple will not accept shipments from outside the country so you must physically take it back to the country of purchase.

If you wish to take advantage of LTE speeds, check this carefully

http://www.apple.com/ipad/LTE/

The USA AT&T model iPad (A1459) is actually a poor choice for just about anywhere in the world other than the USA and Canada, in terms of LTE bands supported.

you would do better to get the A1460 model which while it does have a CDMA radio, it also has a GSM radio.

Or have seomeone there to whom you can ship it and trust enough to manage things for you.

That still goes right to your point about cost effectiveness...it does not take long to wipe out any and all savings in the purchase.