Gardiner Houlgate's specialist watch and clock sale at Corsham this month turned up a tremendous surprise – a Rolex 5517 Royal Naval Special Boat Services Submariner wrist watch which sold to the Rolex agent Haywood Milton of Liverpool for £55,000.

Sent in by a South Coast jeweller, the watch was bought over the counter some eight or nine years ago at its going rate of around £1,000. Over recent years, whatever else has been going on internationally, prices for these models have soared among collectors worldwide.

The jeweller's decision to sell, after it had been stored in the company safe ever since it had been bought, came after a member of staff latched on to its considerable value after viewing a similar watch on the internet.

Auctioneer David Hare was approached and able to confirm its rarity, originality and value, and it went in with an estimate of £40,000 to £60,000.

These watches were commissioned by the Navy for the Special Boat Services in the Seventies; this one was officially issued in 1978 and had unique military reference numbers on the back.

Around 1,000 of these models were produced, but for some reason, only about 300 are still known to exist. We know the men who wore them were engaged in dangerous work, but here's hoping there's a harmless reason for their rarity today.