mumbai, Oct. 4 -- Retail investors borrowing money from brokers to buy shares have been doubling down on some of India's worst-performing blue chips, in the hope that these stocks will bounce back despite steep declines over the past year. Stockbrokers offer a so-called margin trading facility (MTF) for investors to borrow funds to buy shares. MTF refers to an arrangement where an investor buys stocks by partly using their own money and partly by borrowing from a broker. Four of the top five stocks in the MTF book by value-Jio Financial Services Ltd, Tata Consultancy Services Ltd, Tata Motors Ltd and Reliance Industries Ltd-have fallen 13%, 31%, 22%, and 3%, respectively, over the past year, National Stock Exchange (NSE) data show. Hindustan Aeronautics Ltd is an exception; its shares rose 1.32%. NSE's total MTF book, meanwhile, surged to about Rs.99,000 crore on 1 October from Rs.68,004 crore on 7 April, when the Nifty 50 declined 3.4% because of escalations in the global trade war unleashed by US President Donald Trump. Over the past year, the benchmark index has declined 1.4%. Market experts warn against using margin loans to invest in stocks that have been in the red for long. "We think the MTF book exposure towards nonperforming stocks is not sustainable as the recent phase of sell-off in stocks would have triggered margin calls," said Ankit Soni, associate vice president at brokerage and financial services platform Mirae Asset Sharekhan. Falling share prices trigger margin calls where traders either close the position or infuse further money. In such a situation, shares bought with borrowed money lose value, and the broker demands more money from investors to cover the shortfall. Retail investors hold on to sliding blue chip stocks expecting an eventual reversal in fortunes, but the outcomes may not work out, according to market experts.Let's illustrate with an example. An investor buys shares worth Rs.1 lakh with Rs.25,000 from their own funds and Rs.75,000 borrowed from brokers. If the share price rises 10%, the value of the investor's holding would increase to Rs.1.1 lakh....