It depends on what side of TV production you want to get into.
Ads etc (working for an Advertising Agency): try Hillary at White door - 020 7297 9800 or contact the big agencies direct.
Production Co. (Ads & Promos): Get a copy of The Knowledge or FFX (7226 6646) and contact the Production Co's direct or you can try Hillary as above.
TV Companys (CH4 - BBC - ITV): Most run courses which will help, or most have recruitment depts.
What ever you wish to do, unless you're an established director be prepared to start as a runner or assistant.
Good luck.