I have also come accross these guys, while I have never used them, they seem quite professional. I am interested in their business offering which involves a full consultancy service on improving energy efficiency rather than just doing the ratings, afaik that includes equipment specification, and installations, integration with other services etc.
Personally I think that is a badly needed service in the construction industry, as most of the energy products (solar, underfloor, heat pumps, pellets etc) are promoted mainly by manufacturers/distributors rather than installers. As a result the product may not be correctly specified for particular house or may be not propoerly integrated with other services. However I am not sure that for domestic projects people will be prepared to pay for this service.
There is a growing number of other young (and hungry) energy consulting companies. If you can get a list of those expected to become approved BER assessors from SEI this may be a good place to start.
J2K