Why the positive change of bank rate makes the gbp down at the time of release?
Just before any major news, the large institutional traders will sell high, pushing price down. Then, when the news officially breaks, they will buy at the new lower price they caused and the price will go up. Then they will sell again after price goes up. This causes pullbacks on higher time frames.
It also provides all the liquidity necessary for the coming move in the opposite direction by taking out all the stops of us little retail traders.
Of course, it the news means price should go down, reverse this process.