I have posted free adds on uk's local free add sites.do you think it will help in increasing traffic or conversion.

Yup it may help increase your traffic! :)

Free classifieds work, but they are not as good as paid sites. As there are so many such sites, and their traffic is not so much, you cannot expect immediate returns, but in the medium to long run, you get a lot of clicks.

Try to post your ad in as many free sites as possible. (removed self-promo link to the site with the same name as the poster)

Google Base (base.google.com) works in a similar way except for the fact your free listing appear almost immediately and in many cases, above both natural and paid search results.

Perhaps this is good information to know?