The Part P VRQ (should you attain it) claims to give you the right knowledge as regards current safety and legal standards for domestic work only.
As for the practical side, this seems to be what most course providers offer more or less:
Pre work survey/inspection
Safe isolation procedures
Identification of unsafe electrical situations
Earthing and bonding requirements
Electrical test procedures
Cable and component selection
Installation and replacement of electrical components
Checking the correct and safe operation of installed electrical components
Recording of electrical test results and completion of certification
Installing and/or rerouting cables
Special Locations
New circuit requirements
Installing Domestic Lighting Circuits
Maintaining Domestic Electrical Installations
Basic Understanding of 3 Phase Supplies
The more reputable course providers won't let you enrol unless you have a decent amount of knowledge regarding basic household electrics and how to install fittings etc safely.
Simply passing the VRQ would never give anyone all the knowledge & ability to do everything relating to domestic electrics, that's not possible, but I don't doubt that some will think they can.
As for progression, if someone wants to stay doing domestic only there isn't many other qualifications needed from what I can work out (assuming the trainee has 2382, 2392/1 already), it's experience they need.
If they intend to go on site or industrial/commercial it's a different ball game, although a 2391 is well respected it seems