* FTSE 100 up 0.7 pct
* Prudential rises after results
* Ashtead suffers double downgrade
* Slumps in Restaurant Group, G4S hit mid-caps (Adds detail and quote, updates prices)
By Kit Rees and Alistair Smout
LONDON, March 9 (Reuters) - Britain's top share index rose on Wednesday, boosted by a rise in insurer Prudential after it announced a special dividend with results that beat expectations.
Prudential rose over 4 percent, among the top FTSE 100 risers, after its profit was lifted by strong performances at its British, U.S. and Asian life businesses.
"Overall Prudential remains in good shape and... has allayed investor concerns on management's ability to deliver on strategy," said Atif Latif, director of trading at Guardian Stockbrokers.
"The announcement of a special dividend and 5 percent increase of the ordinary dividend has been well received."
Britain's FTSE 100 index was up 42.44 points, or 0.7 percent, at 6,167.77 points by 1209 GMT.
British mining company Glencore recovered some of the previous session's heavy losses to trade up 5.4 percent.
"We could find that the bounce today is fairly short-lived and it starts to shift back down again. Around these sorts of levels, you'd think Glencore is probably in no man's land," Manoj Ladwa, head of trading at TJM Partners, said.
Shares in energy provider SSE also rose, up 1.8 percent after JP Morgan upgraded its rating on the company to "overweight" from "underweight", citing a ""diversified, defensive, cash-generative business mix".
Among fallers, luxury goods company Burberry Group dropped 6.1 percent, almost entirely reversing gains made in the previous session on bid rumours, as HSBC cut its rating to "hold" from "buy".
Construction equipment rental company Ashtead was down 3.2 percent after it was downgraded to "underperform" from "outperform" by Credit Suisse.
"(We) conclude that, independent of the demand outlook, risks are building around rental rates," analysts at Credit Suisse said in a note, slashing its target price to 770p from 1300p. Berenberg and JP Morgan also cut their target price on the stock.
Mid-caps underperformed blue chips, with the FTSE 250 index down 0.1 percent, hit by disappointing updates from Restaurant Group and G4S.
Restaurant Group fell nearly 18 percent to its lowest in two years after providing a disappointing outlook for the forthcoming year.
G4S dropped 13.3 percent after it took an extra charge related to British government contracts.
"Security group G4S failed to woo investors with an increased dividend as attention remained fixed on losses on its government contract to house asylum seekers," Russ Mould, investment director at AJ Bell, said in a note.
Among risers, Cairn Energy rose 9 percent after announcing better-than-expected results from a well in Senegal. (Editing by Toby Chopra)