Britain's FTSE dips below 5 year highs on dividend drag

* FTSE 100 index falls 0.1 percent

* Ex-divs weigh while RSA tumbles after slashing dividend

* BHP Billiton struggles but Rexam gains on profits

By Alistair Smout

LONDON, Feb 20 (Reuters) - Britain's leading blue-chip index dipped in early trade on Wednesday as a number of heavyweight firms traded ex-dividend, leaving the FTSE tucked just below 5-year highs hit in the previous session.

Ex-dividend factors took around 8 points off the index, enough to take it into negative territory, as Barclays, Carnival, GlaxoSmithKline and Reckitt Benckiser RB.L all traded without entitlement to their latest payout.

Glaxo took the most points off the index in early trade, with Barclays and Reckitt also among the top 6 companies putting a negative dent into the FTSE.

By 0845 GMT, the FTSE 100 was down by 4.02 points, or 0.1 percent, at 6,375.05, having risen 1 percent to post its highest close in five years on Tuesday.

The strong close saw it ride up against resistance at the top end of its recent range. The index has been trading between 6,200 and 6,400 for the last month.

"Having re-entered that zone where we slowed up last week, that could prove a bit of a near-term hurdle. These current levels might prove a little bit troublesome," Mike van Dulken, head of research at Accendo Markets, said.

"I don't see much upside, but the markets just don't want to correct back. However, I'd rather hold off and wait for a decisive break of 6,400 before jumping in right now."

Leading fallers was RSA Insurance, down 13 percent in volume of 3 times its 90-day average only half an hour into the day's trade after it slashed its dividend.

"Whilst management states that it wants to keep powder dry for opportunities to grow, the top line growth of 5 percent in 2012 is hardly stellar," analysts at Banco Espirito Santo wrote in a note.

"With our expectation of similar growth in 2013 we expect the dividend cut will likely draw questions on a number of areas, not least longevity of reserve releases, pricing outlook and capital position."

BHP Billiton also suffered after reporting earnings, the global miner losing 2.4 percent after it reported a 43 percent drop in half-year profit and replaced its CEO.

Other earnings reports saw more favourable newsflow. Beverage-can maker Rexam Plc gained 5.4 percent, leading FTSE 100 risers, after it reported a marginal rise in full-year underlying pretax profit, helped by growth in the Americas. (Reporting by Alistair Smout; Editing by Toby Chopra)