The Planning and Building Regulation Approval Process
It's important to ensure that your extension conforms to Building Regulations and you are expected to arrange the necessary inspections. A benefit of conservatories, one of the factors that has led to the explosion in their popularity over the last couple of decades, is that they do not need building control approval. Getting the approval costs money, the exact amount depending on the size and nature of the job, but assuming all the contractors have done their jobs properly, there shouldn't be any undue delay or problems.
Make Sure You Know Who's ResponsibleIt's important to decide who is responsible for making sure that the work conforms to the correct regulation in each case. It may well be the builder, if they are going to take overall responsibility for the job and arrange the other trades by sub-contracting. But if you manage the build and hire the individual builders and contractors yourself, then you may be responsible.
You might be able to avoid this by writing an expectation that work should conform to current Building Regulations into the contracts with each contractor, but then there are rarely written contracts between tradesmen and customers. Either way, as the owner of the property, you will be served with any enforcement notices if an inspector finds issues with the build, so the responsibility is ultimately yours.
Approval ProcessBuilding Control approval can be done in two ways, the first of which is to submit detailed plans to the local authority building control service to pre-approve, but that's really for large buildings and developments. The method usually used for smaller projects is for the work to be approved as the project progresses, starting with the submission of initial plans. The approval on the job can be done either by local planning office inspectors or independent inspectors approved by the government. It is up to you or the builder to arrange these visits so make sure you both know who's doing that.
You can also get approval by making sure that the individual trades are sufficiently qualified. If they have the relevant 'Part' qualification for their trade (e.g. 'Part P' for electricians) then they are qualified to approve their part for the job once it has been finished. Depending on the nature of the job you still may require an inspector to visit to approve the overall project and your local building control authority, which is often at the county council offices, can advise you on this. If you need to get an independent inspector, you can find a list of the approved inspectors belonging to the Association of Consultant Approved Inspectors at their website: www.acai.org.uk
Dangers of Avoiding ApprovalFailure to get building control approval can result in heavy sanctions. Although inspectors cannot force you to change things that they do not think are compliant, they can refuse to give the approval certificate and then, unless another inspector passes the work, the local council can take out enforcement notices to force the work to be rectified. The local building control authority can also choose to take the person responsible for the work to the magistrates' court, where a fine of up to £5000 can be levied, and further fines of up to £50 for every day thereafter, until the work is made good.
Getting your extension through building control approval is a must for any but the simplest of building jobs. Although you might think that you can get away without it by keeping quiet, when you come to sell your house the buyer's solicitor, if they are any good, will find out there's no certificate for the work done and it could render the house unsaleable.