I just phoned and was told that people are currently automatically updated to 10mbps if their exchange supports it and they're on 4mbps, since it's in its 'pilot stages'.
When I asked if the guy could tell me if the exchange is 10mbps capable anyway he just shrugged me off, telling me "if you're on a 4mbps line and the exchange supports it you'll automatically be set up to get up to 10mbps service".
I hate people like that. I'm going to phone again in a bit, see if I can get someone else on the line that's a bit more compliant, as I don't doubt that 4mbps users aren't automatically upgraded - I mean, if they have 4mbps but their connection to the exchange can only realistically get up to 6mbps, wouldn't that be potentially bad for the client on account of a noisy connection?
*edit*
After phoning again I got through to a lady that actually took my number to check the exchange with, and she said it's still limited to 4096kbps max. Checked on my router and the only modulation it can get a connection on is G.Dmt, so I'm guessing we don't have ADSL2+ yet, and so no 10mbps :l oh well