GBPJPY like various other yens has rallied for a considerable period and caused a huge divergence in the mean or average value. This is why the extension from Key Moving Averages is so apparent.
1) From a technical 'value' perspective, short side bias prevails (see below).
2) Sentiment bias - no real shift in reasoning not to buying GBP over JPY due to mon policy. However, Intervention likely at some stage to halt the advance and its speed.
IF you are going to trade this you have risk on either the short, or long side. Shorts favoured, but they need to be extremely risk averse (very small, spread out).