In the UK, it takes between 8 months and 20 years, depending on many factors. In any event the important date is usually the date of filing the patent application. From the day the application is filed, the applicant can disclose the invention at least to the extent that it is described in the patent application, for example, by offering products incorporating the invention for sale. The significance of grant of the patent application is that the patent becomes formally enforceable in court. Within the range referred to above, it is to an extent up to the applicant how quickly the process proceeds. There are three different ways to get a UK patent now, by January 2014 there may be a fourth and a number of variations on each. Experienced expert guidance is very beneficial.     QUESTION HERE

In some circumstances, it can be an advantage to keep a patent application pending because your competitors will be kept uncertain of your rights.  

You do not own an invention until you have patented it. An invention must be secret when you make an application.  OK TO ADD THIS HERE?