* Gives no details on timescale of surprise review
* Union says U-turn raises questions over Lloyds strategy
* Lloyds shares up 3.3 percent at 1430 GMT (Adds details, union reaction, shares)
LONDON, Aug 19 (Reuters) - Lloyds Banking Group, Britain's largest retail bank, said on Wednesday it was reviewing a decision to close all branches of its Cheltenham & Gloucester unit, surprising employees and investors.
Lloyds Banking Group, 43 percent owned by the UK government, had said in June that the 164-branch network of C&G, which specialises in mortgages and savings, would be closed in November as part of a shake-up of its loan operations.
The bank declined to elaborate on Wednesday on the reason behind the move, and gave no details on a possible timescale for the review.
Some 833 full-time positions would have been cut as a result of the closure, with 928 employees losing their jobs. They will now remain in place while the bank considers its options.
"Today's announcement comes with no warning and will make the workforce wonder whether their bosses have any long-term strategy for the future of the bank," said Rob MacGregor at Unite, one of the unions representing C&G employees.
Unite has demanded an urgent meeting with Lloyds to clarify "the format and timescales of the review".
Shares in Lloyds, already higher after an earlier upgrade from analysts at Royal Bank of Scotland, gained further ground in afternoon trade on hopes the review could mean a sale of C&G -- appeasing potential EU concerns over its market share and raising much-needed cash for the loss-making bank.
At 1430 GMT, the shares were up 3.3 percent at 99.9p, against a virtually flat FTSE index.
C&G, previously a building society, was taken over by Lloyds in 1997, triggering windfalls for its members. (Reporting by Lorraine Turner and Clara Ferreira-Marques; Editing by Rupert Winchester)