British Airways owner IAG pulled the UK market lower as investors reacted to the weekend’s IT failure.
Shares in IAG dropped 4% as the airline group counted the cost of three days of disruption, which led to the cancelation of thousands of flights.
BA says it is now operating a full flight schedule at Heathrow and Gatwick.
The benchmark FTSE 100 index fell back from Friday’s record closing high, dropping 47.35 points to 7,500.28.
Shares in the London Stock Exchange group edged up 0.4% after the company said it had agreed to buy a fixed-income platform from US bank Citigroup for $685m (£535m).
On the currency markets, the pound edged down 0.1% against the dollar to $1.2832, but rose 0.2% against the euro to 1.1520 euros.