Shares in Paddy Power Betfair (PPB) have jumped to the the top of the FTSE 100 as the bookmaker confirmed it was in takeover talks with US fantasy sports website Fan Duel.

The shares rose 6.6% to £82.70 on the news of the bookmaker's plans for US expansion, just days after a court ruling that could unlock the betting market in the world's largest economy. The FTSE 100 was up eight points at 7,731.

Paddy Power said it was in talks over a potential merger of its US business with Fan Duel, which operates paid-for fantasy sports competitions.

The US Supreme Court on Monday backed New Jersey's bid to legalize sports betting, taking the US a step closer to allowing sports gambling in a number of states, rather than just selected places like Las Vegas.

Paddy Power was joined at the top of the FTSE 100 by Micro Focus (MCRO), up 6.4% at £13.49 as the software company provided some relief to investors hurt by March's profit warning with news of a $40 million (£30 million) licensing deal.

Smurfit Kappa (SKG) fell to the bottom of the FTSE 100, down 5.2% to £29.42 after US packaging company International Paper (IP.N) said it would not make a hostile bid for its rival. 

Centrica (CNA) dropped 4.1% to 142.3p after a downgrade from analysts at Morgan Stanley.

On the FTSE 250, HomeServe (HSV) surged 9.2% to 828p on bullish notes from UBS and Stifel.

Crest Nicholson (CRST) tumbled 9.5% to 446.8p as the house builder cut forecasts, blaming rising construction costs and flat house prices.

Marston's (MARS) was another heavy faller, down 9% at 101.9p after the pub group swung into a first-half loss.

Among 'small-cap' stocks, Arrow Global (ARWA) tumbled 11.6% to 279p as Berenberg started coverage of the debt purchase and asset management business with a 'sell' rating.