Andrew Aston raided dozens of homes

In the aftermath of the case, Mr Aston, from Smethwick, set up his own organisation dedicated to highlighting the dangers of drugs.

He has now written personally to the Prime Minister Tony Blair and Prince Charles.

But in an angry letter to Liberal Democrat leader Charles Kennedy, Mr Aston said he was "disgusted and dismayed" by the debate at the party's spring conference.

"You will no doubt be aware of this horrific case and as the father of this evil person I shuddered and felt totally incensed by the party's policy regarding drugs."

Mr Aston said he was not opposed to the use of drugs for medicinal purposes, but any other purpose "would only contribute to increasing the ever-growing problem we have in this country".

Mr Kennedy did not take part in the debate or vote on the issue at the conference.

Andrew Aston was only caught when he tried to attack a 92-year-old man and was arrested.

Speaking about his son, Mr Aston said: "Although he is my own son and I love him, we can't have that evil out there."