Welcome aboard! I take it you are referring to Sunderland England, not Sunderland Massachusetts or Sunderland Vermont, both of which are in the northeast part of the US. Most (though not all) people on this board are in the United States, and there are some differences between the US LEAF and the UK LEAF, but I'm sure we would like to hear about your problem and try to make suggestions. So tell us more.
By "switching off" do you mean that the dashboard and center console are both going black? Are there any beeps or chimes when this happens? Has it ever happened when you are moving? (That would be scary!) Does it happen in Park? Neutral? Drive? Reverse? Were you fully powered up before it happened? i.e. was there a green car in the middle of the dash with a double arrow under it? Were you doing anything like pushing on the brake or touching something in or next to the center console? Could your key fob have been pressed against keys in your pocket that ended up pushing one or more of its buttons? Mind you, none of these things should cause the car to power down, but they might provide a hint.
Offhand, this sounds like a really serious and unusual defect that would call for the vehicle to be loaded on a truck (or lorry or whatever you call them) and taken back to the dealer.
End of April 2013: Traded my 2011 SL for a 2013 S with charge pkg.