If you have been affected by the recent British Airways (BA) computer systems failure you may be entitled to compensation for disruption and additional expenses. In the first instance you should seek compensation from British Airways. This is because EU flight compensation regulations require airline operators to provide compensation to passengers that suffer long delays or cancellations in circumstances like this.
If you have travel insurance you may be covered for some expenses (such as the cost of food while delayed at the airport), usually payable where you are unable to claim them back from another source, such as the air carrier. So, in the first instance, you should make any claim for these to BA.