negative interest rates do not result in people spending more. it just results in them moving their funds to a different method of storage that wont charge them.

there is no rational reason why BoS would do this as it ultimately would lose them business.
EG a deposit of £1m equates to a allocation of £10m that BoS can fractional reserve themselves.
so while they hope to collect £40k if the depositor stays with them. but the reality is that the depositor will take out the £1m and go elsewhere and then BoS cannot loan out £10m which even at a standard mortgage rate of 5% would have yielded them £500k in interest

i feel something else is going on behind the scenes because if i can work out that charging someone £40k has a risk of losing £500k.. then they should too
i feel something else is going on behind the scenes because BoS has said they want to stay in the EU. so making Euro holding depositors leave them is the opposite to wanting to stay involved in the EU.

either way its not going to be good for BoS and depositors will just move their funds out...
.. which the op is presuming 'may' be into bitcoin.

personally i dont think there will be a big bitcoin buy-up due to BoS, but the news itself of stupid idea's banks come up with that have no rational reason, or proves that banks are bad.. can only be a good thing for real asset holders like bitcoin