Hi Astara,
My experience may be different to yours, as one of my references didn't answer any virgin calls, it was all delayed and i eventually rang virgin up to find out why it was taking so long.
So for me, It was about 3 or 4 months before they emailed me for the Medical. As they had put me in a "talent pool" as they don't recruit over Christmas.
When they ring for your medical, you usually have to do it asap.. so for me they rang me on a Thursday and i had my medical booked in for Monday. The quicker you do your medical the quicker you get through.. They will contact you usually 2 - 3 days after medical exam.