UPDATE 3-FTSE 100 rallies as trade talks progress; share sale hits Standard Life

* FTSE 100 up 0.6 pct

* FTSE 250 up 0.1 pct

* Standard Life Aberdeen falls on discounted share offer

* Plus500 slips, discloses "drafting error" in 2017 accounts (Adds company news item, updates to closing prices)

By Muvija M and Shashwat Awasthi

Feb 15 (Reuters) - Britain's FTSE 100 rose for a fifth straight session and posted its third straight week of gains amid a broader rally in global markets on Friday on news of progress in the Sino-U.S. trade talks.

The midcap index meanwhile saw online trading platform Plus500 PLUSP.L fall sharply on a report that it may have "misled" investors over losses.

The FTSE 100 .FTSE added 0.6 percent and the midcaps .FTMC closed 0.1 percent higher, with investors seeing little change in the Brexit backdrop after Prime Minister Theresa May's latest defeat in parliament on Thursday. and healthcare stocks -- often deemed attractive in times of economic uncertainty -- contributed to early gains as weak U.S. retail sales data and more downbeat data from China fanned worries about the health of the world economy.

Though initially tentative, the blue-chips strengthened as Washington and Beijing signalled progress in their negotiations, with talks set to resume next week in Washington. The index is on track for its best month since April 2018.

But CMC Markets analyst David Madden said a bounce-back in global equities since late December appeared to be losing steam.

"Some of the ground that has been made up in the last 7-8 weeks could actually be handed back in the near term," he said.

Royal Bank of Scotland RBS.L added 2.4 percent after announcing a better-than-expected dividend and reporting a more than doubling of 2018 profit. Life Aberdeen SLA.L slumped 6 percent on its worst day in a year after a discounted share offering.

On the FTSE 250, shares in Plus500, which lost nearly one-third of its value this week following a profit warning, tumbled after the Times newspaper reported https://www.thetimes.co.uk/article/cee7454c-30a1-11e9-b26a-04579b7820b3 that the company may not have informed investors about a $103 million hit from client trading in 2017.

"After poking in a massive profit warning out of the blue, this (the Times report) adds further mistrust about management" a trader said.

Plus500 later confirmed it had made a "drafting error" in its 2017 accounts, but said the error would not impact previously reported revenues, profits or the balance sheet. stock fell 12.2 percent to more than a year low and dragged peers IG Group IGG.L and CMC Markets CMCX.L lower.

Restaurant Group RTN.L , which slumped in the last session after announcing a CEO departure, added 2.5 percent after a Berenberg rating upgrade, while Domino's Pizza DOM.L shed nearly 3 percent after a downgrade by the brokerage.

Premier Foods PFD.L ended 1.2 percent lower, having skidded as much as 6.3 percent after dropping plans to sell its dessert brand, Ambrosia.