UPDATE 1-Amec says trading in line

* Order book 3 bln stg at end-Oct vs 3.2 bln end June

* On track for 2010 EBITA margin of 8.5 percent

(Adds details)

LONDON, Nov 12 (Reuters) - British energy services firm Amec (AMEC.L) said it was trading in line with expectations although its order book had shrunk slightly since the end of June.

The company, which said in August it expected a stronger performance in the second half, said it expects an EBITA margin approaching 8 percent in 2009 and was on track for its stated target of 8.5 percent in 2010.

Its order book, which it said was "conservatively stated", stood at 3 billion pounds ($5 billion) at the end of Oct, comapred with 3.2 billion in June.

"Amec remains on track to deliver another year of improved performance in 2009 despite the ongoing challenging external environment," Chief Executive Samir Brikho said in a statement on Thursday.

Shares in Amec, which have soared 75 percent since the start of the year, closed on Wednesday at 866 pence. (Reporting by Victoria Bryan) ($1=.6033 Pound)