SNC-Lavalin (SNC.TO) will not raise its offer for British engineering and construction firm WS Atkins unless it faces a rival bid for the British firm, the Canadian construction and engineering group said on Monday.

SNC-Lavalin agreed to buy WS Atkins last month in an all-cash $3.6 billion deal, at a price of 2,080 pence per share.

U.S. activist investor Elliott Capital Advisors bought a 6.8 per cent in WS Atkins a day after the terms of the deal were announced.

The offer will only be increased if a third party announces a possible or firm offer for WS Atkins, SNC-Lavalin said in a statement.