The sister of a British activist killed in the Gaza Strip in 2003 has slammed the decision to release the man responsible early as “incredibly sad”.

Sophie Hurndall, whose brother Tom was shot while volunteering in Rafah for the International Solidarity Movement, said the family was “angry and shocked” to hear that Taysir-al-Heib would leave jail 18 months before his sentence expires.

Ms Hurndall told the Ha’aretz newspaper that the family had feared this would happen, despite the fact that three previous appeals by Mr al-Heib to have his sentence commuted had failed.

She added: “Since my brother was killed I have lost faith in humanity. I cannot believe that people can do such things, and that my own government can sit by and keep quiet."

Tom's mother, Jocelyn Hurndall, also criticised the decision. She told a radio station that it showed Israel was more concerned with herself than the pursuit of justice.

Mr al-Heib, a former Israeli soldier, was jailed in 2005 for manslaughter, obstruction of justice and giving false testimony. He was sentenced to eight years for the "unlawful killing" of the 22-year-old.

But an army committee said he had changed, was no longer a threat and agreed to release him.

The committee’s decision to grant early release came despite warnings from Israel’s Military Advocate General that it would hurt relations between Israel and the UK.

A spokesperson for the British Foreign Office said: “We recognise the grief this decision will cause to the Hurndall family.