It depends on the price action after you submitted the order, the type of order you submitted, and also the bid/ask spread at the time the order was processed.
The ask price is the price you pay to buy the shares. If you come to sell them at some stage you will be offered the bid price: this will be lower than the ask at that time and the difference is the spread, which is profit for the broker. If the spread was widened by the broker, perhaps because of some news expected or just released, or just the closing/opening time market volatility, the bid and ask prices will change.
If your order was a stop order, the broker will execute it when their ask price reaches the level you specified.
If you specify a buy order and price jumps (gaps) 22p higher, then the broker would be unable to process your order between 266 and 288, as there was never a quoted price in that range. so they would execute it at the first available price at 266 or above (which obviously in this case means at 288).