Sorry im a little late here
As this is my specialised area.
Forget national average your general downstream speed is defined by the target SNR set within the attenuation of the line, this based openreach circuits adsl/adsl2& adsl2+ circuits over a **copper** pair from the exchange to your nte your main socket.
The attenuation of the line is a calculation made from lenght of pair and gauge of metalic path this has the biggest impact on speed.
However on the above circuits 95% of them are not set up for adsl as years ago it didnt exist. In the industry it was called star wiring which for a pstn dc voltage capaictor setup was fine ** now broadband has changed all that**.
In the uk we lack behind in general broadband speeds due to we were more advanced before as a pstn/dacs.
As for virgin what they offer is a FTTC product which is only co-ax in to your premises not the full fibre product as advertised shock along with this people that fit and repair this without minimal understanding or technical ability along with self employment paid per job.
As bezzer has mentioned BT infinty is openreachs role out of the fibre to the cab ie the FTTC, we will also offer the FTTP product which would be a fibre directly into your premises which would mean no more pstn service only voip.
Would the FTTP product take us to no1 (maybe up there buisness users) for residential the future will be a secure wireless network which openreach better start looking at!
Your internal wiring config will affect your connection 100% unless is a proper nte2000 or ssfp setup. Even if you plug your router in to your nte **test port** and notice no speed increase your profile may be capped so wouls req removal from your cp.
** some of openreach network contains ali lol **
** You current setup will not be optimum for any dsl product
**
** The nte test port will only work if wired correcty **
A decent site for questions on your adsl connections
http://www.kitz.co.uk/ it has good info the tech side is a little basic
I have helped a few guys off here feel free to drop a pm about your dsl connection to me.