Richard Desmond-owned N&S bought Channel 5 from the German broadcaster RTL Group in 2010 for £103.5 million, but after three years of cutting costs out of the business and rising ad revenues, it is expected to be worth much more.
It is understood that the business could be worth in the region £700 million to £900 million.
The process is at an early stage and N&S has not yet decided whether it will definitely sell the business. In 2011, Desmond, who is the chairman of N&S, did not make any divestments, despite hiring Barclays Capital to make a valuation.
Channel 5 made a profit of £20.6 million in the first six months of 2013, a turnaround form a loss of 16.1 million in the same period of 2012.
A spokeswoman for N&S declined to comment.