According to figures collated by the BSE, while BPL Refrigeration a non-specified group stock has been trading at a new 52-week high for the past three consecutive sessions, BPL Engineering has risen by 30 per cent in four trading sessions and BPL Sanyotec has also risen steadily to breach the crucial barrier of Rs 10 on May 18.

Market sources, highlight the role of Calcutta line operators in jacking up the prices in the midst of rumours of bonus and mergers.

According to BSE sources, although the most important criteria for slapping margins, is the price rise and the actual number of trades conducted at the counters, these stocks have been under the microscope because of the nature of trades.

As per SEBI guidelines, the exchange is permitted to slap a special margin upto25 per cent of the previous closing price of the stock. ``Margins are not only used to curb any speculative influences but also take care of the volatility at the counter in the following sessions,'' explained a source.

Besides the 25 per cent limit specified by SEBI, the exchanges also have the powers to impose an inch over that limit if the circumstances call for such an action, which BSE has done before in stocks like CMC, Videocon, BPL and Sterlite.

BPL Engineering has been moving steadily from a low of Rs 13.05 on May 8 to trade at a high of Rs 17 on May 18, within a span of six trading sessions. The volumes at the counter have also seen a sharp rise of over 1,400 per cent during this period. Most interesting feature of this jump has been the spread of trades, and the number of shares offered during a single trade.

On May 8, while the counter recorded a volume of 2,700 shares traded, it was spread in the form of 168 shares over 16 trades. However, on May 18, the huge chunk of 42,900 shares werespread over 97 trades with each trade recording the quote of over 442 stocks.

BPL Refrigeration on the other hand was locked at Rs 23 on the BSE, on May 19 with a huge volume of 1.14 lakh shares. The stock has been recording new 52-week highs from May 13, from Rs 13.90 to a high of Rs 20.95 on May 18.