Now in many countries, not only in UK, people open a credit line to buy BTC, because there is a real chance to buy and wait when it goes to the moon again. Due to this, banks are in panic (little bit), but they will not fight against BTC
What do you mean by the bank will not fight against bitcoin,the banks have already banned the use of credit cards to purchase crypto currency and that includes bitcoin, 
with the price going up to $20k and now coming down to well below $8k is a huge difference and the banking system is afraid that the users will mess with their card investing in crypto to earn a quick profit and getting stuck.