That is if you're interested in some of the research, theory, and results of the "basic" level of DSM (which we all call DLM). In the future, Vectoring also plays its part in this.
Here's what I found while searching for some references to BT's approach to DLM:
As for BT's DLM (and them chairing the various workgroups on it): BT has got a good research group, and do a lot of work at making the technology work when deployed in a widespread world (ie not just blue sky work, or kept in the lab). Their DLM is probably an output of this work.
For example, I've come across this before: Muse report on "Enhanced DSL Algorithms" (2005)
However, I just found this: Muse report on "Static and Dynamic Spectral Management Analysis" (2006)
BT seem to call it DSM rather than DLM, and I've seen it referred that way elsewhere (and referenced as DSM level 1 - where vectoring is considered to be DSM level 3).
Using that as a search, I've found the following references too:
Access Network, UK NICC ND 1513 (2010-01).
 Dynamic Spectrum Management (DSM), NICC Work Item 308 – under
 Vectored VDSL performance in the UK, NICC Work Item 309 – under
 Specification of the Access Network Frequency Plan applicable to
transmission systems connected to the BT Access Network, UK NICC ND
The last part in particular gives us a hint of what NICC might end up reporting on relating to DSM and vectoring.