Employment And Conflicts Of Interest?

An Anonymous Coward in a difficult position asks: "I recently have been offered a position / job with a rather large company. The position is also rather high profile. The opportunity is great except for one thing. The person trying to hire me is currently a client of my current employer. The opportunity was presented to me because my current employer has pretty much scoffed at the offers made by this client and they do not take this client seriously. The client then came to me and asked for my help. This help is slowly developing into the above mentioned opportunity. What if any are the legal implications of all of this?"