With a bank, you can be pretty confident you can go to an ATM and get small amounts of money out, but even there we've seen system failures block withdrawals for longer than this one. Also, there's small daily ATM limits and at least one major British bank has a policy of refusing large cash withdrawals (several thousand pounds or more) full stop through any means unless you can prove to their satisfaction why you need that much cash: http://www.bbc.co.uk/news/business-25861717