Britain's FTSE boosted by an unsolicited bid for Smurfit Kappa

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* FTSE 100 up 0.9 pct

* Smurfit Kappa jumps 17 pct on unsolicited offer

* Sector peers Mondi and DS Smith rise

* Just Eat set for worst trading day

LONDON, March 6 (Reuters) - An unsolicited bid for Irish packaging group Smurfit Kappa from U.S.-based International Paper lifted shares in the whole sector on Tuesday, providing a boost to Britain's top share index.

The FTSE 100 was up 0.9 percent at 7,180 points by 0907 GMT, slightly higher than the European average as world markets shrug off trade war fears or political risk concerns in Italy following its inconclusive general election.

Shares in Smurfit Kappa, Europe's largest producer of paper-based packaging, jumped 17 percent to 33.7 euros after the company said the offer from International Paper failed to reflect its growth prospects and the industry's attractive outlook.

"We believe an offer above 33 euros per share would be realistic" to start discussions between both groups, Jefferies said in a note where it saw a "positive M&A read" to packaging peers DS Smith and Mondi MNDI.L>.

The two groups, also listed in London, rose 4.5 and 3.9 percent respectively and were among the session's top gainers.

UK testing company Intertek Group secured the second-best position up 6.1 percent after publishing its full-year results.

Things went very differently for Just Eat, which disappointed investors with its 2018 core earnings forecast and was set for its worst trading day ever, down 12.5 percent.

Just Eat said it would invest an additional 50 million pounds to stay ahead of its food delivery rivals, a figure which surprised some investors.

"If we were honest we did not expect a figure for total investment for 2018 to the magnitude of 50 million pounds," Berenberg analysts said.

Another loser was Industrial equipment rental company Ashtead Group whose shares were down 4.9 percent after it released third-quarter results. (Julien Ponthus Editing by Peter Graff)