Luke, a little addition to Beekie's info; the J1 visa is only good for three years and you cannot return for another 2 years.
Inome tax is not payable for the first 2 years. The UK tax people don't like this so it all gets paid in the third year. WMU have just issued a bonus in the third year which will go some way to paying this.
I think that you are from Godzone and if I recollect your tax bods are worse than the UK lot. Therefore I would suggest not informing them that you are working at all - just on permanent holiday once you are overseas.