The 17th Edition of the IEE Wiring Regulations redefined the zones for electrical equipment in bathrooms and must be used for installations designed after 30th June 2008. They are now identified from 0 to 2, with 0 being the wettest - the previous zone 3 is no longer defined.

Zone 0
The interior of the bath or shower which can hold water.
Zone 1
The area directly above zone 0 limited vertically to 2.25m above the bottom of the bath or shower.
Also 1.2m horizontally from the centre of a shower outlet to the height of the outlet or 2.25m whichever is the higher.
Zone 2
The area beyond zones 0 and 1, 0.6m horizontally and up to 2.25m vertically. Zone 2 also included any recessed window with a sill next to the bath.
Note:

• Protection
  All electrical circuits within bathrooms must be protected by Residual Current Devices (RCD) not exceeding 30mA. This applies all electrical equipment whether it is controlled a switch in the bathroom or remotely switched.

Electrical equipment may be identified as having a certain level of mechanical and moisture protection, these are quoted as 'Ingress Protection' (or IP) numbers - such as 'IPXY', where X and Y are numbers, the X showing the level of mechanical protection and Y showing the level of moisture protection - in both cases, the higher the number, the better the protection. If a piece of equipment does not have an IP number, it must not be used in zones 0, 1 or 2 (or elsewhere having a wet/damp environment).
Typical electrical items which are marked with IP numbers include:

Shaver power points are not IP rated, however, if they comply with BS EN 60742 Chapter 2, Section 1, they can be located in zone 2 (or beyond) providing they are unlikely be be the subject of direct spray from any shower.
As well as IP numbers, items may be classed as PELV or SELV.

Standard electrical wall fittings (such as wall sockets, flexible cord outlets and fused switches etc.) are not IP rated so cannot be installed within zones 0, 1 or 2. No standard socket outlets are allowed within 3m of the outer limit of zone 1, and any socket fitted would be on a RCD protected circuit.

Any electrical item approved for use in a zone may be used in another zone with a higher number, but not in a lower number zone.
Zone 0
Requires electrical products to low voltage (max. 12 volts) and be IPX7 (the mechanical protection is unimportant).
Zone 1
Requires electrical products to be IPX4 or better, or SELV with the transformer located beyond zone 2.
Zone 2
Requires electrical products to be IPX4 or better, or SELV with the transformer located beyond zone 2.
Beyond zone 2
When the size of bathroom extends beyond zone 2, portable equipment is allowed, however they should be positioned such that that their flex length does not enable them to be used in zone 2.

Competent person (Electricity at Work Regulations)
The following is the definition lifted from the Electricity at Work Regulations regarding a competent person:
"No person shall be engaged in any work activity where technical knowledge or experience is necessary to prevent danger or, where appropriate, injury, unless he possesses such knowledge or experience, or is under such degree of supervision as may be appropriate having regard to the nature of the work."
The statement from the EAWR is very broad and is often the most confusing aspect of the whole electrical industry. As of yet, there is no legal structure behind being competent in terms of qualifications and experience. It is fair to say though, a relevant qualification would be a distinct advantage in a court of law.
Competent person (Building Regulations)
Competent persons schemes were introduced by the Government to allow individuals and enterprises to self-certify that their work complies with the Building Regulations as an alternative to submitting a building notice or using an approved inspector. It enables companies to register with a recognised organisation and speed up the process as well as monitor domestic work.
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Building regulations are made under powers provided in the Building Act 1984, and apply in England and Wales. The current edition of the regulations is ‘The Building Regulations 2000’ (as amended) and the majority of building projects are required to comply with them. They exist to ensure the health and safety of people in and around all types of buildings. They also provide for energy conservation and for access and facilities for disabled people.
You are responsible for making sure that the work complies with the regulations if you are carrying out building work personally. 
If you are employing a builder, the responsibility will usually be theirs - but you should confirm this at the very beginning. You should also bear in mind that if you are the owner of the building, it is ultimately you who may be served with an enforcement notice if the work does not comply with the regulations.
Remember - complying with Building Regulations is a separate matter from getting planning permission for your work.
The Building Regulations contain various sections dealing with definitions, procedures, and what is expected in terms of the technical performance of building work. For example, they:

Part P does not apply in the case of all buildings. It applies to all fixed electrical installations after the suppliers’ meter in buildings or parts of buildings comprising:

While Approved Documentation ‘P’ applies to all electrical installation work in dwellings, it is not necessary to notify building control bodies in the following circumstances:

* Clarify this with your local Building Control before commencing work. Although Part P was designed to enforce standards and increase safety, many council offices simply do not understand the implications of the document and merely insist you are part of a competent persons scheme. This is not true but you do need to notify before you begin work on an installation.