You can complete minor electrical jobs, without any electrical qualification.
(alterations/additions to existing circuits)
Any electrical work in kitchens and bathrooms become a different kettle of fish.
I have never been on "a domestic installers course" but I am a domestic installer and approved part contractor.
There two levels of scope
If your electrical skills a trade specific:
Then
Defined Scope (Level B) – best suited to those businesses that do some electrical work in the course of their main business (i.e. kitchen/bathroom fitters, builders, gas fitters, plumbers etc). You will only be assessed in the areas of electrical work you typically undertake and will only be able to certify work that you have been assessed against.
or I your aim to do fully electrical installations:
Full Scope (Level A) – ideal for fully qualified electricians whose main business is electrical installation work. Allows certification of all types of domestic work.
Most scheme providers will expect at at least the 2382 City and Guilds qualification, some expect much more such as 2391 C&G
There is guide here
http://www.partp.co.uk/downloads/GuidetoPartP_August2009.pdf
You will have to take an have days assessment with evidences of your work.
Don't be fooled in to thinking these type of courses allow you, on completion to self cert work.
There may be of value to you personally, if you are a complete novice and give an in sight in to the requirements of BS7671 and Part P of building controls.
But it is not the route I would be taking to become a competent person.
You need to be taking a more in depth course.
PS. Part P is a building Regulation, you don't need to take a course on it, just learn and understand it's contents.