The TVDJA is your best bet, if you wish to Join an organisation, there is nothing dodgy about them (Apart from Mike's Suits!), and they welcome new members from all over the UK, whether you are new to the business or have many years experience - all are welcome to join.
Mike spends a lot of time helping people here on DJU, and I think that in itself shows a lot of personal dedication to the industry he, and the TVDJA represents, which is why I have no hesitation in recommending them, I've also yet to hear a bad word said about them.
The TVDJA website can be found
HEREAlso consider membership with the Musicians Union, there has been some doubt about whether they accept membership from D.J's, but I can pesonally confirm that they do. The Musicians union offers a lot of membership benefits such as legal advice, Contract & Agency Advice and more interestingly cover of £10m Public Liability insurance included in the membership fee. Membership fee's are tiered depending on what your yearly (DJ) income is, although this is going to be scrapped in the New Year, and a different fee structure implemented. At the moment I would anticipate that most D.J's would currently pay around £78 - £150 per year to join. Students in full time education can get the same cover for £33 a year if paid by direct debit!.
The Musicians Union Website can be found
HEREBeing a member of a professional organisation looks good to your clients, whether you state the fact on your literature or website, since it shows dedication, increases your professionalism and does wonders at giving peace of mind, and can often pay for the original membership fee five times over

in increased business and peace of mind.
Personally given the option of joining DJU / Musicians Union or advertising in the Yellow Pages, then the membership would be given the first priority. Personally I chose the M.U, but this was purely a
personal decision and in no way a reflection of the TVDJA.