The family of a former Royal Marine have failed to get enough signatures to get the UK government to put pressure on France over his murder.

The body of Carl Davies, who worked at Sittingbourne Community College and later at the Isle of Sheppey Academy before joining a security firm tackling piracy, was found on the south Indian Ocean island of Reunion in November 2011. He was just 33.

A petition for the UK to raise the case with the French authorities was created in January after the release of Vincent Madouré, who was found guilty of Carl’s murder.

He was convicted after a trial in the island’s capital Saint-Denis last June, but was released in October after his appeal for a retrial was successful.

The petition needed 100,000 signatures to be considered for debate in parliament but, on Wednesday last week – its final day – it had reached only 11,472.

Carl’s sister, Kerrie Stewart, 37, said: “I really don’t know what happens next. If I’m being honest with myself this fight is more or less over. I’m not sure what else we can do.

“We’ve tried everything we can, we’ve gone above and beyond but, unfortunately, we’re so tied by foreign law, I don’t think we’re going to get anywhere.

“The petition was to try and get the British government to get behind our plight but we’ve got to accept our government is not going to help us.”

In May, when the petition got 10,000 signatures and The Foreign and Commonwealth Office was obliged to respond, it said ministers and officials did not interfere with the judicial processes of another country.

Kerrie said: “We feel abandoned, isolated by a very dysfunctional system that we call our government, which my brother fought for years for. But we are not defeated. There comes a point when you’ve got to move on, but we’re not going to stop seeking justice for Carl.”

Mrs Stewart thanked all those who had got behind the campaign. “I just hope, after seven long years of fighting, they will still remain behind us for what should rightly be, and that’s justice for Carl.”