* Britain's FTSE 100 index is seen opening up 23 to 25 points, or 0.5 percent higher on Friday, according to financial bookmakers, extending the previous session's strong gains in tandem with leaps on Wall Street and in Asia. Hopes that central bank meetings next week will take - or at least point to - more steps to support struggling major economies underpinned the gains. For more on the factors affecting European stocks, please click on