UPDATE 2-Aegon underlying earnings disappoint, shares fall

* Q3 underlying earnings 351 mln euros vs 437 mln expected

* Q3 net 145 mln euros vs average 108 mln in Reuters poll

* 154 mln euros tax gain reverses four quarters of losses

* Takes 43 mln euro UK provision for potential over-charges

* Shares down 3.6 pct, underperforming index

(Rewrites throughout, adds CFO, analyst comment, shares)

By Gilbert Kreijger

AMSTERDAM, Nov 12 (Reuters) - Third-quarter underlying earnings at Dutch insurer Aegon (AEGN.AS)(AEG.N) fell short of analysts' expectations after the company took an unexpected provision for British pension products, sending its shares down sharply on Thursday.

Aegon reported a 30 percent drop in underlying earnings to 351 million euros due to exceptional items, such as reducing its equity and credit market risks and the UK provision for potential over-charges.