The beating that the Royal Bank of Scotland took today is not the sole reason for Sterling’s sharp downmove. The market is really nervous about which other big institution is sitting there with a load of worthless assets. ( As an amusing aside, this quip, also from the FT, says it all:

HM Treasury to stock market: “We stand ready to bail out banks”
Market to HM Treasury: “YOURS!”

Now where is Sterling likely to go? A fifth wave target is around 1.6850. Sterling chart I expect good sellers to show up on any recovery to 1.7730-60 levels. So if you are still holding any GBP positions, you should consider selling them on any direct recovery to that window.