Why is the pound Morgan Stanley's top G10 short?

Morgan Stanley keep faith with the GBP bear trend in their latest weekly FX bulletin

Morgan's still see mucho downside for the pound and see cable rolling over to 1.30 by year end as the decline has only just begun.

An increase in vulnerability to external shocks, market volatility and a decline on global trade has ramped up their bearishness on the quid. Brexit concerns loom large but they say they won't increase until the referendum date is set

The like to play shorts in GBPJPY while using rebounds to sell GBPUSD. They highlight 1.40 and then 1.38 as key downside levels

Speaking of Brexit, a poll from ICM is just out and has 42% voting to stay vs 40% voting to leave. I firmly agree with MS that the real trade won't start happening in earnest until we get a date