Ah indeed - I over simplified to make a point. But there is still a cost.-0.40% only applies to small portions of deposits (as most is lent out via mortgages etc) and only applies to certain banks as not all have surplus deposits. PTSB for example do not have any surplus deposits
Irish Bank can borrow at -.4% in market, or at 0% from customer. They'd prefer to borrow at -.4% than 0%.
In UK, borrow from market at 0.7%, or from customer at 0%.
Advantage in UK is still >1% compared to Irish Banks.