Electrics are essential to modern living and to many of the comforts and appliances that it would be hard to do without. Maintained in good order, it is a resource that we daily take for granted. If it fails, it can cause fires or shock. Regular testing (now advised at each change of ownership) is essential. For landlords, there will be a duty of care to ensure that electrics of their properties are properly maintained and safe.
Most domestic properties have been on single phase supply and circuits comprise live, neutral and earth. Live carries the power, neutral completes the circuit, and earth provides the protection of diverting faulty current safely away.
In 2005, it was made a requirement that electrical work in buildings, plus garages and outbuildings should comply with the standards laid down in the Wiring Regulations. This meant that a qualified electrician should complete the work. You should look for an electrician to be NICEIC registered. Anyone attempting DIY work would need to be approved on a Competent Person Self-Certification scheme or submit a building notice application to the local authority to advise them of what work is to be carried out.