Malaysian drug courier Yong Vui Kong, who was spared the gallows after a string of unsuccessful fights against his death sentence, is now challenging the caning regime in Singapore.

Yong, 25, was re-sentenced in November last year to life imprisonment and 15 strokes of the cane. This followed changes to the law which give judges the discretion to impose life terms and caning, instead of the previously mandatory death penalty, for drug couriers who help the authorities in a substantive way.

However, Yong filed an appeal last week, asking for his caning sentence to be quashed.

His lawyer M Ravi is challenging the constitutionality of caning, in particular the manner in which the punishment is carried out.

Mr Ravi is also arguing that Yong is being made to suffer a greater punishment than was prescribed by law at the time he trafficked in drugs. He contends this is because, before it was changed to make the death penalty discretionary, the law did not provide for caning for drug traffickers at the time.

Yong was 19 years old in 2007 when he was arrested for trafficking 47.27g of heroin. He was convicted in November 2008 and given the then-mandatory death penalty.

Yong filed an appeal but later withdrew it. However, he changed his mind and in 2009, Mr Ravi revived his appeal on the grounds that the mandatory death penalty was unconstitutional.

Mr Ravi's subsequent bids in court to overturn the death sentence all failed, but as a result of the numerous challenges, Yong lived to see changes in the law that ultimately spared his life.

This was because in 2011, the Government began a review of the death penalty laws and Yong was among the 35 death-row inmates whose hangings were put on hold.