You can try two ways as they sometimes give diffrent information (as in my case)
Go to www.virginmedia.com make sure you are not signed in, click on Virgin Broadband, TV & Phone tab and then enter your postcode (dont choose your own house number as you will be recognised as an existing customer pick a house number that you know is not with virgin and it will tell you weather 100Mb/s has been enabled.
Why do I say try it this way?
Because when I wanted to upgrade, via change my services it said I could not get the 100Mb/s service but when doing it the way I just explained it had 100Mb/s available, so I then had to phone up the thinking of leaving us dept (because standard customer service reps will say NO) yet these guys will sort it out for you.
Some parts of VM get the info updated before others, you will just have to keep checking online every day, mine was enable over a month before official due date as were many other areas.
