Only getting 2.3mbps on cable

I'm visiting my parents who have virgin media cable broadband. They've had it for a couple of years, and are only on the basic package.
When they first signed up, the basic speed was 2mbps, but I know that's been notched up to 10mbps - however their connection is running at only 2.3mbps according to the speed checker on this site.
Why would this be the case?
Was it necessary to speak to their customer services in order to get them to adjust the line speed when the "upgrade" happened?
I know it's unlikely you'll ever get the full speed advertised, but surely 2.3mbps compared to 10 is rather poor?
Cheers
bb.

Would have thought the upgrade would be automatic - maybe some very old modems don't cope with that well?

I'd speak to them and see what they say.

If their PC had been heavily optimised for a 2Meg service (RWIN tuning) then it may need to be done again.

802.11b wireless (and to a lesser extent G) can limit you to this sort of speed sometimes.

Also some very old routers cannot cope with routing a 10Meg connection, let alone a 50Meg connection.