Fault tolerance with Web services (BGP/DNS-RR?)

Hi experts,

I need your advice. I am responsible for the network for a 24x7x365 company who requires their online services to be always available under www.ourdomain.co.uk. The web applications are run in-house on Windows Server 2003 servers on multiple Internet connections. The current setup is:

www.ourdomain.co.uk is the primary connection and resides on a cluster of servers (or web farm) on the office DMZ and is accessible from the outside via an Interoute leased line.

www2.ourdomain.co.uk resides on a second cluster of servers (or web farm) on the office DMZ and is accessible from the outside via a VirginMedia cable line (secondary connection).

This provides us with redundancy in that if any server on either cluster dies, the applications keep on running. Also, if the Interoute connection dies, customers can access www2.ourdomain.co.uk.

However, the powers that be want it so that our customers do not need to go to www2 - in fact, we drop this name altogether. It needs to be that if www.ourdomain.co.uk is unavailable (because Interoute leased line has died), then www.ourdomain.co.uk just redirects automatically to the IP of the VirginMedia line (which is currently www2.ourdomain.co.uk).

I'm vaguely aware of BGP and DNS Round-Robin, but I'm not sure what the best solution is for us. If I go down BGP/DNS-RR avenue, this means relying on our ISP. So my question is:

Is there something WE can do to provide this additional redundancy? If not, what/who is the best service provider to go to who can provide us with this level of service, with a high level of fault tolerance and which involves little or no change to our current DNS/IP/ISP set up?

Thanks

Jon