(Close): Worries over prospects for the eurozone weighed on banking shares, helping to drag the FTSE 100 lower.
Investors were rattled by gains for anti-austerity parties in Spanish local elections over the weekend.
Worries are also persisting over whether Greece will be able to meet upcoming loan repayments.
However, Royal Mail was having a better day, with its shares jumping nearly 3.6% to 521.50p following a broker upgrade.
Cantor Fitzgerald upgraded its rating on Royal Mail to "hold" from "sell", and also increased its target share price to 500p from 440p.
AstraZeneca shares fell 2.2% after Amgen said it was ending a collaboration with AstraZeneca over developing a psoriasis drug.