I was initially very alarmed by this post, followed quite quickly by a healthy level of skepticism:
I live in the UK, I bank with Santander & I have sent money from my account to exchanges to buy Bitcoin. Santander have not closed my account or contacted me about my activities.
Remember, correlation does not equal causation. The letter doesn't explain why they are closing this person's account; we don't know anything else about this person's banking activities and we are just jumping to a conclusion based on a few data points.
Until I'm made aware of this happening more (possibly even to myself) then I don't feel comfortable drawing the conclusion that Santander are trying to stamp out the use of Bitcoin.