* Lloyds gives 12-mths notice on competition concerns
* Standard Life says worth less than 5 pct of 2017 revenues
* Shares in Standard Life Aberdeen down 4.8 pct (Adds detail from statement, analyst reaction, share price, bullet points)
LONDON, Feb 15 (Reuters) - Standard Life Aberdeen said on Thursday it had been served notice by Lloyds Banking Group and Scottish Widows on a 109 billion pound ($153 billion) asset management deal, further denting shares in the recently-merged group.
Clients have pulled billions of pounds in assets from SLA in the six months since Standard Life and Aberdeen Asset Management formed one of Britain's biggest asset managers.
The merger triggered the right for Lloyds and Scottish Widows, which is part of the British bank, to review an agreement struck in 2014 for Aberdeen to manage assets on behalf of Lloyds' insurance and wealth units as Standard Life is a "material competitor" to both.
The mandate, to invest in largely lower margin passive equity and fixed income assets, makes up less than 5 percent of SLA's revenues, but could still leave a hole of up to 140 million pounds to be filled, analysts said.
"We are disappointed by this decision in context of strong performance and good service we have delivered," Keith Skeoch and Martin Gilbert, Standard Life Aberdeen's co-chief executives, said in a statement announcing the review.
Scottish Widows and Lloyds said in a statement they had given notice to SLA of their plans to terminate the deal, kick-starting a 12-month process to find a replacement provider or providers. SLA said it planned to participate in the process.
SLA said it would take a one-off impairment charge of 40 million pounds and its shares were the weakest performer on the blue-chip FTSE 100 at 0935 GMT, with a 4.8 percent fall.
"The real question ... will be the extent to which Standard Life Aberdeen can shed costs to offset the likely loss of revenue," Bernstein analyst Edward Houghton said in a note.
Exane analyst Arnaud Giblat said the relative underperformance of SLA shares ahead of the Lloyds move, and the small chance it could retain the mandate at a lower margin, would act to cushion the fall. ($1 = 0.7120 pounds) (Reporting by Maiya Keidan; editing by Silvia Aloisi and Alexander Smith)