Eh no, there are better ways you can help the homeless. Volunteer for organisations that help these people. Give tinned food to the homeless shelter, volunteer at the YMCA, volunteer and help at the AA and CA, and other organizations that help with addiction. Going up to a homeless guy and just handing him a tenner isn't helping him/her.
No one really "gives money" to the homeless, they give change which is usually less than 30p and comes in the form of useless pennies in your pocket.