CORRECTED-FTSE 100 steadies after Saudi attacks; Sirius Minerals plummets

(Corrects first bullet point to up not down)

* FTSE 100 up 0.1%, FTSE 250 drops 0.4%

* Sirius Minerals sinks to record low

* HSBC and Prudential weigh on the main index

Sept 17 (Reuters) - London's FTSE 100 index inched higher early on Tuesday as a sell-off over the implications of the weekend attack on Saudi Arabian oil facilities eased in Europe, while shares in UK fertilizer mining venture Sirius Minerals tanked.

The FTSE 100 gained just over 0.1%, with heavyweight oil majors continuing to feel the benefit of a rise in oil prices since the attack on Saturday on the world's biggest crude processing plant.

The midcap FTSE 250, however, fell almost 0.4%, with Sirius Minerals diving 60% after it said it would slow development of its polyhalite project and scrap a planned $500 million bond sale as the UK government declined to provide support to facilitate its financing. (Reporting by Yadarisa Shabong in Bengaluru; editing by Patrick Graham)