The FTSE 350 Travel and Leisure sector was 0.7 percent lower, with airline IAG down 1.5 percent.

Other travel groups such as TUI and cruise operator Carnival fell 2.8 percent and 1.6 percent respectively, while Intercontinental Hotel Group dropped 1.6 percent.

Among mid-caps, tour group Thomas Cook fell 4.3 percent. It said bookings were lower than last year due to uncertain geopolitical conditions, but prices were holding up and it was sticking with its annual guidance.

"(Events in Brussels are) clearly and understandably going to dent consumer confidence and it's making life very difficult for the travel companies and the airlines, and that was evidenced with Thomas Cook today, they (had) a very cautious trading update," Wyn Ellis, director of travel and leisure equity research at Numis Securities, said.

"The problem now is that we're having a whole series of these events, and until they stop, the fear is that they're going to continue."

Britain's FTSE 100 index was up 0.1 percent at 6,192.74 points at its close, having touched its lowest level since March 11 in early trade.

Gold rose after investors flocked to safety, boosting precious metals miners Randgold and Fresnillo, which were up 1.6 percent and 1.4 percent respectively.

Likewise chemicals company Johnson Matthey and Shire were the top risers, both gaining over 2.5 percent as investors took shelter in defensive stocks.

"The actual recovery was more notable in the defensive sector rather than the more risky assets ... it isn't really a return of risk appetite, it's more a case of finding the safest haven for your money," Brenda Kelly, head analyst at London Capital Group, said.

Among the top fallers, however, outsourcing group Capita slipped 2.3 percent on a downgrade from Stifel to "sell" from "hold", which cited concerns over organic growth potential and its M&A strategy.

It was joined by banking group Barclays, down 2.1 percent after investment bank Goldman Sachs cut its price target on the stock, citing weaker investment banking revenue trends and the planned disposal of Barclays Africa.

Among mid-caps, Sports Direct slumped 10.5 percent after its founder Mike Ashley warned on profits for 2016.

(Additional reporting by Kit Rees; Editing by Alison Williams)

By Kit Rees and Alistair Smout