Spend any time in central London and perhaps, like me, you've noticed an increase in the number of bodies lining the streets. I'm talking about the shadowy, recumbent figures of the homeless. Statistics bear this out: the government's own show a rise last year of 14% in homelessness and 23% in rough sleeping.

The last government increased funding for homeless shelters but also kept the homeless out of sight by criminalising them. Various laws and antisocial behaviour orders (asbos) were used to make central London streets more pleasant for those with a bed to go to.

When I was homeless no one could arrest me for it. Now all rough sleepers know they are only safe from arrest outside the asbo line, so they sleep just beyond it. You can find the line simply by walking London's streets at night.

The coalition government has continued to criminalise the vulnerable, sad, addicted and sick who make up most of our homeless population. It has also cut funding for services by more than 25%. Since homeless people are the opposite of the Olympian ideal, God only knows what measures they will experience to keep them out of sight this summer.

Homeless people present the thoughtful Guardian reader with a dilemma. It's hard to walk past the hollow-eyed guy who looks like he hasn't eaten for a week without putting anything in his paper cup. On the other hand, your money could be spent on the drink or drugs that fuel his self-destruction.

One woman, who feared that by giving money to a homeless man she was banging another nail in his coffin, recently told me that she had instead given him an apple. I replied that he didn't need an apple; he almost certainly needed drink or drugs to blot out the reality of living on the streets – which is unhealthy, dangerous and frightening – as well as to help him forget the reasons he's there. No one is homeless by choice.

It's OK by me if a homeless person spends my money on drink or drugs. When I was homeless I found it very hard to beg, but people who did give me money were preventing a crime, because the money meant I didn't have to steal in order to eat or to feed my addiction. And, frankly, it's none of your business where an addict is on his journey. If your money funds the final hit, accept that the person would rather be dead. If your act of kindness makes him wake up the next morning and decide to change his life, that's nice but not your business either.

Your business is to know that money desperately needed by someone went directly into his hand. Pause before you give your earnings over to those smiling, healthy, legal street beggars: charity chuggers. I know from experience that a high proportion of donations is wasted on administration and on the public relations machine that persuades us what a good job the charity is doing. The employment opportunities the charities create are not among the people they claim to help. No, the money goes to employees far removed from poverty, further excluding the target group.

Before you give, find out how much of your money will be delivered to the people you want to help. Since historically charities' income isn't public money, an inappropriate level of accountability remains. At least the money I give to a street beggar leaves my hand and reaches his before another large, greedy hand can snatch most of it away.

• Mark Johnson, a rehabilitated offender and former drug user, is an author and the founder of the charity User Voice