With regards to the existing Building Regulations, how is a 'competent firm' that is to deal with electrical work defined?

Planning and Architecture Part P Electrical
2

This is defined as electrical contractors who conform to the following standards:

·     in accordance with the requirements listed within BS7671;

·     those contractors whose work has been independently assessed by a third party;

·     contractors that have been actively registered under the NICEIC Approved Contractor scheme and the Electrotechnical Assessment Scheme.