I must admit, i tend to agree with a lot of Irish_steve says.
A lot will depend on who you work for, if you join a handling agent there will be more oppurtunities to climb the ladder quicker, but as steve says that may require making the right connections, if you join an Airline then progress will be slow if at all as no one leaves the top jobs.
Security also determines that it will be quite unlikely that you will get to speak to crew and even if you do again they will tell you very little.
Also many airlines are constantly looking to outsource, virtually all of Heathrow has now outsourced with the exception of BA,UA, AA & AC, who like i say the people at the top don't leave.
Virgin also handle themselves but their ops are at LGW, Load control is done by BKK and they just do turnaround co-ordination at Lhr, though they do have a traffic office.