By Carla Mozee, MarketWatch

LONDON (MarketWatch) -- Shares of Weir Group PLC climbed in London on Tuesday, outperforming a slim gain for the broader market, following a ratings upgrade for the engineering company.

The FTSE 100 index finished the session 0.1% higher at 6,829.17, adding to Monday's gain of 0.1%.

Weir shares leapt 2.5%, topping the U.K. benchmark index, after being upgraded at Credit Suisse to outperform from neutral. Analysts said Weir could see a roughly 10% upside in fiscal 2016 pretax earnings in part on improving upstream oil-and-gas markets.

But shares of rival IMI PLC fell 1.9% as Credit Suisse downgraded them to neutral from outperform, saying Weir "offers a better relative risk return profile over a two-year horizon," than IMI does.

Elsewhere, most supermarket stocks advanced after declines on Monday. Tesco PLC picked up 2.4%, as new Chief Executive Dave Lewis told employees in a staff email the company will address its loss in market share "with urgency," according to news reports. J Sainsbury PLC gained 1.8% and Wm Morrison Supermarkets edged up 0.4%. Marks & Spencer Group , however, turned 1% lower.

Shares of miners BHP Billiton PLC (BHP) and Rio Tinto PLC rose 0.8% and 0.2%, respectively, paring heftier gains.

An upside "production surprise" looks to be in store at the Escondida copper mine in Chile, in which BHP has a 57.5% stake and Rio Tinto a 30% stake, said Deutsche Bank analysts in a Monday note. A strategy to run three plants at the mine may be adopted by the companies in 2015, which could increase earnings at BHP and Rio Tinto by 2% to 3% in the next couple of years, the analysts said.

Shares of SSE PLC fell 1.7%. The utility company on Monday said it will sell gas transporter SSE Pipelines Ltd. to the Environmental Capital Fund for 52.7 million pounds ($87.08 million).

From the data front, Markit said construction output in the U.K. increased by its fastest pace in seven months in August. The construction purchasing managers' index came in at 64.0, up from 62.4 in July, and above a 61.0 consensus estimate. The housing, commercial and civil engineering markets each logged sharp growth last month, said Markit.

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