The failed rescue operation caused a diplomatic row between Britain and Italy after Italian president Giorgio Napolitano said it was "inexplicable" that Downing Street had not alerted Rome to the plan to rescue the men in advance.
But Foreign Secretary William Hague insisted it had been impossible to inform the Italian authorities in advance.
Mr McManus, 28, was working for the construction company B.Stabilini when he was kidnapped on May 12 by gunmen who stormed his apartment in the city of Birnin-Kebbi, about 110 miles away from Sokoto.
Mr Lamolinara was also abducted. A German colleague managed to escape by scaling a wall, but a Nigerian engineer was shot and wounded.
More top news
Former shadow foreign secretary Hilary Benn led calls by a series of senior Labour MPs urging colleagues to 'win' back the party.
A team of detectives and specialists is set to begin a painstaking excavation of the area where Ben is thought to have gone missing in 1991.
The foreign secretary's suggestion last week's bombing of an aid convoy might constitute a war crime prompted an angry response from Moscow.