UK-listed banking stocks felt the brunt of the sell-off on Thursday as concerns about Portugal's financial sector prompted investors to scale back risk appetite.The retreat followed widespread pressure across European equity markets after a missed debt payment by Espirito Santo International, the parent of Espirito Santo Financial Group (ESFG) which is, in turn, a major shareholder on Portugal's largest bank Banco Espirito Santo (BES). Shares in both ESFG and BES both tanked in Lisbon before being suspended from trading.Fears about contagion sparked a drop in Portuguese bonds today with the yield on benchmark 10-year notes rising 16 basis points to 3.92%. Bond yields in other so-called 'peripheral' Eurozone nations were also on the rise today."The situation in Portugal has the potential to place the whole Eurozone banking system under further stress, especially as it heads into an era of increased scrutiny by EU regulators and the European Central Bank," said Daniel Sugarman, Market Strategist at ETX Capital.In other news, Spanish lender Banco Popular Espanol delayed a planned bond sale today, citing "heightened volatility" in credit markets.London-listed banks RBS, Barclays, HSBC, Lloyds and Standard Chartered were all out of favour this afternoon.Top performing sectors so far todayPersonal Goods 22,934.82 +1.31%Real Estate Investment Trusts 2,715.34 +0.14%Bottom performing sectors so far todayChemicals 9,821.52 -2.40%Technology Hardware & Equipment 1,023.23 -2.20%Forestry & Paper 10,803.67 -2.15%Household Goods & Home Construction 11,192.89 -2.09%Banks 4,173.01 -2.03%BC