UK's FTSE edges up, helped by Scottish stocks, after dismal week

* FTSE 100 up for first time in six sessions

* Scottish-exposed stocks up as poll shows "No" voters lead

* Investors avoid large index bets before referendum

* BP (LSE: BP.L - news) shares briefly spike, traders suspect "fat finger" error

* Aveva down almost 25 percent after warning on FX hit

By Tricia Wright

LONDON, Sept 12 (Reuters) - Britain's top shares rose for the first time in six sessions on Friday, helped by companies with Scotland exposure, after another poll showed a majority would vote against independence.

Shares (Frankfurt: DI6.F - news) in companies with strong ties to Scotland, such as Royal Bank of Scotland (LSE: RBS.L - news) , Lloyds Banking Group, soft drinks group AG Barr and utility SSE (LSE: SSE.L - news) , all rose as the latest poll put supporters of the union on 51 percent against 49 percent for those who favour independence, excluding people who said they did not know how they would vote in next Thursday's referendum.

But with the 'No' camp holding just a modest lead, investors refrained from making large bets on the FTSE 100. The index rose 11.71 points, or 0.2 percent, to 6,811.33 points by 1422 GMT, in thin trading volume at about half of the 90-day daily average.

The UK benchmark briefly spiked even higher around mid-session, hauled up by a jump in shares in oil major BP , a move which several traders blamed on a likely human error - a "fat finger" trade.

The flurry of activity in BP shares at 1041 GMT saw the shares jump 4.8 percent to 494.9 pence, adding around 4.3 billion pounds (6.98 billion US dollar) to the company's market value. The FTSE 100 shortly after hit a session high of 6,832.16 points. At 1422 GMT, BP shares were down 0.4 percent at 470.35 pence.

After a four-week winning streak, the FTSE 100 was on course to record a 0.6 percent fall for this week, which has been marred by concerns about the Scottish referendum, further signs of slowdown in China and the prospect of a tightening in U.S. monetary policy.

"There's decent buying interest at 6,800, but people are worried about the Scottish referendum and that's stopping them from doing too much," Will Hedden, sales trader at IG (LSE: IGG.L - news) , said.

Whitbread (LSE: WTB.L - news) was the top loser on the FTSE 100, down 1.7 percent, as UBS (NYSEArca: FBGX - news) downgraded the owner of Premier Inn hotels and Costa Coffee to "sell" from "neutral".

Among mid-caps, Aveva Group (Other OTC: AVEVF - news) , whose software is used to design power plants, shipping and oil and gas facilities, tumbled about 25 percent as it warned about a 14 million pound hit to its first-half revenue from currency moves and the phasing of some rental renewals. ($1 = 0.6160 British pound) (Additional reporting by Francesco Canepa; Editing by Larry King)