* Swannell joins board on Oct. 4 as non-exec director
* To become chairman Jan. 4
* Current chairman Stuart Rose to leave company on Jan. 4
* Swannell's salary 450,000 pounds, half of Rose's pay
* Shares up 1.2 percent, outperform FTSE 100
(Adds detail on Swannell's salary, 3i statement, analyst comment)
By James Davey
LONDON, Aug 23 (Reuters) - Marks & Spencer, Britain's biggest clothing retailer, has added some investment banking clout to its boardroom, naming veteran City heavyweight Robert Swannell as successor to chairman Stuart Rose.
Confirming media speculation, M&S said on Monday that Swannell would join the board on Oct. 4 as a non-executive director and become non-executive chairman on Jan. 4.
Swannell, 59, is a former chairman of Citi's European investment bank and vice chairman of Citi Europe and the current chairman of music, books and games retailer HMV Group.
Rose will stay as chairman until the latter date when he will leave the retailer, three months earlier than his previously stated last possible departure date of the end of March.
A spokesman for M&S said Swannell will be paid an annual salary of 450,000 pounds ($701,700) when he becomes chairman, nearly half the 875,000 pounds Rose was on.
"It is a privilege to be asked to chair one of the world's greatest brands," Swannell said in a statement.
He is also a non-executive director of British Land and 3i Group.
In a separate statement 3i said he would step down from 3i on Oct. 1.
Confirmation of Swannell's appointment was welcomed by analysts.
"His appointment makes strategic sense. He knows his way around M&S, retail and the City," said Neil Saunders, consulting director at Verdict.
The appointment completes the restructuring of M&S's board.
Marc Bolland, the former boss of Wm Morrison Supermarkets, succeeded Rose as chief executive in May, while Alan Stewart was appointed finance director earlier this month.
The appointment will also see M&S revert to standard governance practice.
Rose has had a rocky relationship with institutional shareholders since he combined the roles of chairman and CEO in 2008 against corporate governance guidelines.
Rose will depart M&S after six and a half years at the firm. He was initially parachuted into the retailer in 2004 to fend off a takeover approach from billionaire retail entrepreneur Philip Green, a defence that Swannell, then at Citi, advised on.
Shares in M&S were up 1.2 percent at 336.7 pence at 1255 GMT, valuing the business at about 5.4 billion pounds, and compared with a 0.8 percent rise in the FTSE 100 index. (Editing by Mark Potter and Erica Billingham) ($1=.6413 Pound)