Are you using a BT HomeHub Router with your Chromecast ?
If so you will need to disable the smart setup on your Router (see instructions linked below).
Also, make sure that you have the latest Chromecast app and NowTV app on your ipad.
If using a different ISP and Router, then disregard my post about the smart setup feature .
To be honest i am not familiar with the Virgin Router features and not hundred percent certain your can cast to an Android smart TV without a Google Chromecast dongle with the NowTV app ?
I am sure other community forum members who are more familiar with your router and Sony TV will come along and offer you some further assistance.