When ADLSMax (8Meg) starts getting rolled out in April supposedly, you'll start to see higher upload speeds to 768 or thereabouts depending on line level.
As to when the various ISPs will start upgrading and what they'll charge, there's not a lot of information until BT officially announce dates.
At the moment, you'd either have to find a ADSL Max trial or see if your local exchange has been unbundled and has an LLU operator (samknows.com can tell you this) like Bulldog, Wanadoo, Be, UKOnline who offer either an ADSLMax or ADSL 2+ service.
ADSL 2+ (Be and UKOnline to name two offering this in certain exchanges) allows for upload speeds at 1.3MB - and very nice it is too 😉