It started with a global conflict and had all the classic ingredients for a family feud - the death of a patriarch, a cherished heirloom and a stepmother.

At the heart of it is the Military Cross won on the Western Front by First World War poet Siegfried Sassoon.

Once thought to have been thrown into the River Mersey by the poet in a fit of disillusionment over the war, it has re-emerged 90 years later to turn his only granddaughter and his son's last wife against each other.

The medal has now found rest in the Royal Welch Fusiliers' regimental museum at Caernarvon Castle. But the row has left the regiment, currently fighting in Afghanistan, to pay twice what it expected to in order to secure its distinguished brother officer's decoration.

The exchange of vitriol has become public following the death last year of Sassoon's son, George, at the age of 69.

His daughter by his first wife, Kendall, and her two children are the poet's only living blood relatives.

It was his fourth wife, Alison, with whom George - a polymath and something of a character in his own right - spent his latter days. In May, her son by a previous marriage, Robert Pulvertaft, announced he had "discovered" the MC and other possessions of Siegfried's in an old treasure chest in George's mother's house on Mull.

"Like most people I thought it had been thrown into the Mersey," he said. "I found it while clearing out the attic."

The MC and other items were due to have been auctioned at Christie's in London on June 6. An arrangement had been made between Kendall and the Royal Welch Fusiliers to pay £30,000 each for the medal so that it could be put on public display in the museum. But when Kendall returned from holiday with her partner, Stewart Reeves, and their children, they found the medal had been withdrawn from auction. Instead the regiment has paid Alison Sassoon the full £60,000.

Now Mr Reeves has told The Herald that Alison had scotched the original arrangement in order to cut Kendall out of the picture. "She withdrew it because she did not want Kendall to get any credit out of this," he said.

He said the regiment had written to explain Alison had withdrawn from the agreement to sell the medal through their joint bid and offered it for sale on June 6 on the basis that there was no disclosure of Kendall's involvement.

Having sought advice, they did not feel the auction at Christie's could have proceeded legally while the agreement for sale was already in place.

"This uncouples us from Kendall Sassoon's generous offer. As the time for withdrawal approached we were under pressure and in the circumstances the regiment felt it had to accept the new offer," the letter states.

"Unfortunately Kendall's absence on holiday regretfully prevented us from getting her views. Please be aware that we intend to purchase the medal privately for the full £60,000 on a 100% ownership basis, which on reflection is a safer option for the museum."

However the letter adds: "We did not want in any way to break our relationship with Kendall as the granddaughter of one of our most famous officers and would like her to become a lady associate member of our officers' association."

Robert Pulvertaft denied there had been any malicious intent in withdrawing the medal from sale. He said: "We did it when we found out Kendall was putting up half the money because it would be unfair on her children to be paying for it.

"They are beneficiaries of the Sassoon estate, apart from the MC and a few other chattels that went to my mother. He told us before he died to get what we could for the medal, but we thought the regiment would buy it outright. He'd have been furious if he thought the money was coming out of the children's inheritance."