You could have your bonds in foreign currency, not that i am recommending it, but you could have such bonds in your portfolio base on the argument of currency diversification.
There is a also a case of diversification for high yields (junk). those bonds are denominated in USD(which are alot less volatility vs emerging market currencies. And to make things more juicy, the DTA for UK and US on interest effectively reduces it to zero withholding tax. In addition, the huge portion of the bonds in that
Ishare high yield corp bond fund holds BB credit rating bonds.