UBM's outgoing chief executive, Lord Hollick, has tried to sell the 35 per cent stake, but potential bidders have been put off by the asking price.
With Symbian chief executive David Levin replacing him in April, the company is stepping up efforts to sell its non-core assets, which include its television interests, even if this means dropping the price.
Bankers said that UBM would now accept a bid in excess of pounds 150m for the Channel Five stake. Luxembourg-based RTL, which owns the rest of the broadcaster, would be the most likely buyer, although BSkyB has also been touted as a potential suitor.
Lord Hollick, who is joining private equity firm KKR after more than 30 years at UBM, could also be interested in bidding.
UBM also owns a 20 per cent stake in news broadcaster ITN, although this may be even harder to sell. Mr Levin wants the company to refocus on its core publishing and exhibitions businesses.
UBM confirmed last month that it had instructed its bankers, Dresdner Kleinwort Wasserstein, to review its market research division NOP World. The company is understood to have consulted Mr Levin before making the announcement.
Shareholders have questioned the strategy behind UBM's investment in Channel Five and have been pressing management to resolve the issue. After merger talks with Channel 4 failed last summer, a sale is the only alternative.
Channel Five's commercial performance is improving. Its total audience share climbed by 1.7 per cent to 6.66 per cent last year, despite the increased competition from digital channels. It also recorded its first operating profit in February, seven years after it was founded, making pounds 8.5m.Reuse content