* FTSE 100 up 0.2 pct

* Gains in banks offsets weakness in miners and energy firms

* BA up after it agrees to merger terms with Spain's Iberia

By Simon Falush

LONDON, Nov 13 (Reuters) - Gains in HSBC (HSBA.L: Quote, Profile, Research) and energy stocks kept Britain's top share index in positive ground for a third day on Friday, offsetting weaker defensives, while British Airways (BAY.L: Quote, Profile, Research) rose after agreeing a merger with Iberia.

By 1204 GMT the FTSE 100 .FTSE was up 10.82 points at 5,287.32 points, a day after closing at a three-week high. It is on track for its highest close since September 2008.

The index is up 2.7 percent this week and has rebounded 53 percent since hitting a six-year trough in March.

Analysts were confident that the gains were sustainable.