From what you have said it looks like Virginmedia have done some work on your local network and have re-segmented the network, this is the main reason you have a different IP address, this doesn't happen often normally only when there is high utilization or network upgrades.
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Mike's correct - mine did the same a few weeks ago. One thing that will need attention is if you are running a BQM it is no longer pinging "your" connection (but the person who inherits that i.p address!) and so settings need changing.
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-------------------- John --------------------
My services: HD TV on VIP (+ Sky Sports & Movies & BT sport), x3 V6 boxes (1 wired 2 WiFi,) SH2 in modem mode with Airport Extreme Router. On VIVID200, Talk Anytime Phone, x2 Mobile SIM only iPhones.