The pound has breached the initials lows around 1.3215 that were formed right after the drop after the Brexit news. The fact that this low was breached and did not act as support for a sustained rally, indicates that traders anticipate GBP to remain weak for some time. This creates an opportunity as previous support turns to resistance. A short entry should be positioned around 1.3215 - 1.3238. An even more conservative short position would be initiated at 1.3289. At least one of the 200 MAs on the hourly chart will confluence with one of these levels, providing additional resistance barriers to price.
Due to the overall oversold state of the pound, any short position from these levels should be held only over the short-term and not beyond the 1.2800 low ,