The proceeds of the sale will be used to set up scholarships

The iron key was held by Second Officer David Blair who was removed from the crew at the last moment and did not hand it on to his replacement.

Binoculars were used to detect threats to liners in the days before radar.

Titanic sank on her maiden voyage from Southampton to New York on 15 April 1912 with the loss of 1,522 lives.

The conjecture is that this is the key that could have saved the Titanic Henry Aldridge and Son Auctioneers

It is known Second Officer Blair was given a pair of binoculars for use on the ship as he lent them to lookouts for help guiding them into Southampton on the voyage from Belfast.

He was replaced in the post by Henry Wilde who would later perish when the liner sank.

Great provenance

Mr Blair wrote of his disappointment in a postcard sent to his sister-in-law just before Titanic sailed. The postcard is also part of the sale.

In it he wrote: "I shall have to step out to make room for (the) chief officer of the Olympic. I feel very disappointed I am not to make her first voyage."

A US inquiry into the sinking heard evidence from one of the lookouts who said had they had binoculars they would have seen the iceberg sooner and been able to move out of the way in time.

A spokesman for auctioneers Henry Aldridge and Sons of Devizes said: "The conjecture is that this is the key that could have saved the Titanic had it not left the ship.

"The great thing about this key is its provenance - his daughter gave it to the International Sailors Society and when it has been sold the money raised will be used to set up bursaries and scholarships in the name of Mr Blair."