The most senior officer to survive the Titanic attempted to downplay the iceberg collision to secure a £3 million insurance payout, suggest documents which are to be auctioned in Devizes.

Second officer Charles Lightoller insisted he merely felt a "slight jar" when the liner hit a "small low-lying iceberg" in April 1912, after which it sank, claiming more than 1,500 lives.

His account of the disaster was recorded in an insurance claim form, which was signed by the surviving officers of the Titanic after they arrived back in New York.

In the document, titled 'Letter of Marine Protest', Lightoller also attempts to excuse the behaviour of staff who failed to spot the iceberg, denying they were guilty of "negligence".

The four-page legal-sized form, which secured the ship's owner White Star Line a £3 million payout from insurers, is to be sold at auction on April 26.

Auctioneer Andrew Aldridge, of Henry Aldridge and Son, described the lot, expected to fetch up to £12,000, as "fascinating" and "important".

"This document, prepared for insurance purposes, includes an interesting and sometimes curious account of the disaster," Mr Aldridge said.

"It is fascinating that the officers would seem to minimize their encounter with the rather large and ominous iceberg by describing it as a 'small low-lying iceberg'.

"This could possibly have been an attempt to downplay the size of the iceberg due to the question of liability and who was to blame for the sinking."

The unpublished insurance claim was certified and signed by the Titanic's 2nd, 3rd, 4th and 5th officers on April 19 1912.

"All went well until about 11.45pm of April 14, 1912, when in latitude 41-46 North, longitude 50-14 West, the ship came into collision with an iceberg," it states.

"The ship swung to port, but struck a 'growler', or small low-lying iceberg, with the bluff of her starboard bow, making a comparatively slight jar with a grinding sound.

"On examination it was found water was coming into several compartments; all hands were called on deck, the boats were ordered to be cleared, and subsequently filled with women and children.

"At 2.20am April 15 the Titanic sunk, going down bow first in very nearly the same position when struck."

The insurance settlement was paid within 30 days of the sinking.

"To our knowledge, this important document is without equal as we have been unable to locate any prior sale record of such an original account for an insurance claim," Mr Aldridge added.

The lot is one of 200 Titanic collectables included in the auction, which is to commemorate the 102nd anniversary of the loss of the ship.