It would probably be helpful if you said what interests your son has and the type of business sector he would like to gain his work experience in, then any interested local businesses could contact you. I would expect that if you are unable to find a work placement for your son the school will place him into something, which may not fit in with his interests/ what he would like to gain his work experience in. You could try approaching one of the local business "clubs" who meet up to see if they can help, take a look in the publications SEMagazines.co.uk, Around Dulwich, Residential/Living South, possibly Southwark Council or a local charity organisation, one of the many local sports/golf clubs (along Dulwich Common) or Crystal Palace Sports Centre. East Dulwich/Forest Hill is full of local businesses, who just maybe willing to take on an extra pair of hands for 10 or so days.