By Claire Marshall Social affairs correspondent, BBC News

Richard Whelan was stabbed six or seven times

Some decisions must be made in an instant. You can choose to act - or you can turn away.

Richard Whelan decided to confront the man who threw chips at his girlfriend on a bus. He paid for that choice with his life.

Anthony Joseph, who stabbed him six or seven times, has pleaded guilty to the manslaughter of Mr Whelan.

Baggage handler John Smeaton, 31, also made a life-changing decision to intervene.

When suspected would-be suicide bombers attacked Glasgow Airport in June this year, Mr Smeaton was on a cigarette break outside the terminal.

T-shirt slogan

When he saw a man get out of a burning vehicle and start hitting a policeman, he ran to help.

His bravery has turned him in to a celebrity. He has met the prime minister and has inspired the printing of T-shirts with the slogan, What Would John Smeaton Do?.

I think it's time people started realising that the more you turn away, the worse it's going to get John Smeaton

Speaking to the BBC outside Glasgow Airport, where he still works, Mr Smeaton said: "If people are intervening in a serious situation, then they're doing the right thing.

"If they are killed they should be remembered for what they have done.

"Everyone in society nowadays seems to turn away.

"I think it's time people started realising that the more you turn away, the worse it's going to get."

Phil Carroll, 51, from Salford, also made headlines when he decided to take a stand.

He saw a group of teenagers throwing stones at his car, which was parked just outside his home. Mr Carroll challenged them, and was viciously assaulted.

'I would intervene'

He was in a coma for three weeks and is now permanently brain damaged.

But he told the BBC that he would do the same again.

The public should not intervene directly in any situations of criminal activity Home Office advice

"I would intervene - I've had three brain operations - it's made me even harder than I was before.

"I just don't tolerate any kind of nonsense at all now by anybody or anything," he said.

However, his wife Jean thinks it is too dangerous.

"I think the right thing to do is to go in and stop it.

"But now, especially with what they've got in their pockets - especially the younger ones, there's no limit - they will just kill you.

"They know they'll get away with it."

So what is the official advice?

The Home Office provided the BBC with this statement: "The public should not intervene directly in any situations of criminal activity - they may put themselves in danger, exacerbate the situation and ultimately may be acting on the wrong side of the law. "

There are many others who decided that they could not walk away - and paid the price.

Figures from a YouGov survey done in August 2007 show that one third of those who choose to challenge anti-social behaviour are either attacked or threatened.