Thoughtless comments can push gay teenagers to the point of suicide, Liberal Democrat education spokesman Lord Tope said.

"The tragic irony in all this is that many of them have yet to have sex with anyone, let alone a relationship," he added.

Lord Tope said teachers either ignored the bullying of gay pupils or on occasion joined in the persecution.

"We heard of a deputy head in the north of England who, seeing an effeminate 16-year-old pupil standing by the school's Christmas tree called out: 'Robert, shouldn't you be on top of the tree?'

Teachers can contribute to bullying

"An RE teacher in Scotland required by his enlightened school to discuss homosexuality in his classes told the whole class: 'I'm sure nobody wants to know about the poofs apart from Ben'."

The teacher then told the boy he would have to read the chapter on his own, Lord Tope said.

He told the Lords gay schoolchildren faced taunting, vandalism or their possessions and being attacked and beaten up.

The letters he had received from such pupils show these experiences cause many to consider taking their own lives.

A boy from the Midlands wrote: "I tried to take an overdose of pills four times and tried to slit my wrist one time."

Lord Tope urged the government to repeal Section 28 of the Local Government Act, which he said many teachers misunderstood, believing it banned them from discussing homosexuality.