Shares in airlines fell after comments from Ryanair raised fears of a price war in the sector.
Ryanair said it could cut fares by as much as 9% on some routes in the next few months as competition intensified.
Its comments overshadowed news of a 55% rise in first-quarter profits, and Ryanair’s shares fell 3.8%.
Shares across the sector were hit by Ryanair’s comments, with EasyJet and British Airways owner IAG both down by more than 3%.
Shortly after midday, the FTSE 100 was down 75.83 points, or 1%, at 7,377.08.
Household products giant Reckitt Benckiser was another faller, down 2.2%, after it said it still had “work to do on addressing the full implications of the recent cyber-attack”.
The maker of Dettol, Vanish and Durex had already said the attack meant its second quarter like-for-like revenues would drop 2%.
In addition, Reckitt said it was “experiencing tough market conditions”.
In the FTSE 250, shares in discount retailer B&M rose 2.8% following reports at the weekend that it could be a takeover target for Asda.
Shares in Acacia Mining sank 10% after several brokers cut their price targets for the company’s shares.
Acacia – which is the largest gold miner in Tanzania – has been hit an export ban on copper concentrate for processing abroad. Since Tanzania introduced the ban in March this year, the company’s share price has halved and it has suspended its dividend.
On the currency markets, the pound rose 0.3% against the dollar to $1.3039 and climbed 0.4% against the euro to 1.1190 euros.