Bear in mind the people complaining about Virgin are only getting 200-250Mbps on a promised 500Mbps. 200Mbps vs. 20Mbps....
No, the business service is arguably worse than the residential one - there's no network segmentation as it's not possible to do, and the provided cable modem is awful.
If my choice was between 20Mbps FTTC and VM I'd give VM a try. I'd probably not cancel the BT service until Virgin was installed though, and make sure I kept an eye on the cooling off period.
How would it work. Would VM install a cable next to my BT cable?