Shares in the world's largest security firm, G4S, jumped 7.4% after it reported a rise in full-year revenues and profits.
The firm, which is seeking to put a number of historic scandals behind it, said revenues rose 6% to £6.8bn, while pre-tax profits at its continuing businesses climbed 14% to £352m.
G4S shares jumped 7.4%, making it the biggest riser on the FTSE 250.
The benchmark FTSE 100 opened little changed, down 2.89 points at 7,336.10.
Shares in insurer Legal & General dipped 0.5% as the company reported an 11% increase in operating profits to £1.63bn for 2016.
Back in the FTSE 250, shares in funeral provider Dignity sank 13%. The company reported a 3% rise in profits last year to £71.2m, but said it was trimming its earnings growth target in the face of increased competition.
On the currency markets, the pound continued its recent slide against the US dollar, dropping a further 0.25% to $1.2170. Sterling also fell 0.1% against the euro to 1.1531 euros.