By Sara Sjolin, MarketWatch

LONDON (MarketWatch) -- The FTSE 100 moved into the red for a third straight day on Tuesday as investors remained concerned about the outcome of the referendum on Scottish independence next week.

The London benchmark slipped 0.2% to 6,822.49, erasing a small gain from the open.

Scotland referendum: Traders were still nervous ahead of the vote on Scottish independence on Sept. 18 after a poll out over the weekend put the pro-independence camp in the lead for the first time. However, other surveys still point to majority for the "no" campaign.

Economists at Credit Suisse in a note on Tuesday sketched out some of the risks of Scottish independence, saying Scotland would fall into a deep recession. They also noted that the pound would weaken and could fall to as low as $1.50. Read: Pound's selloff on Scottish uncertainty isn't over

The pound (GBPUSD) got creamed in Monday's trade, but was almost unchanged on Tuesday. Sterling bought $1.6113, compared with $1.6110 late Monday in New York.

Data: The Office for National Statistics said industrial production climbed 0.5% in July, beating market expectations of a 0.3% rise.

Rob Wood, chief U.K. economist at Berenberg, called the numbers "solid", but cautioned that growth in industrial production should start to slow over the next couple of months when the "effect of fighting in Ukraine on core-eurozone business confidence feeds through to the U.K."

Mark Carney speech: Investors were also eagerly awaiting Carney's speech in Liverpool, scheduled for 11:45 a.m. London time, or 6:45 a.m. Eastern time.

"Traders often use these public appearances to scrutinize his words to potentially gain further clarity and clues on the monetary policies and any changes in the future," said Sam Fox, financial sales trader, in a note.

Movers: Wm Morrison Supermarkets PLC climbed 3.1% after Citigroup upgraded the supermarkets chain to buy, according to Dow Jones Newswires.

Energy firms declined, with shares of Royal Dutch Shell PLC (RDSB) fell 1.5% and BP PLC (BP) slipped 1%.

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