If you think you have invented something then you can apply for a patent. Your application is immediately read to see if there are any security or other implications which would require it to be classified. Mistakes and serious errors of judgement DO sometimes occur, as in Sir Frank Whittle's case!
On payment of fees a first search is made to see if anything similar to your invention has been found in the archives, national and international.
If nothing is found, or if anything found can be shown to be significantly different, and if your invention is not "trivial", "obvious" or "impossible" (i.e. bonkers in the nut!) a more expensive Substantive Search is made.
For me on one occasion this brought up 2 US Patents for other inventions, but I was easily able to detail significant mechanical and conceptual differences between them and my own and I was granted UK and US patents on this particular invention.
A patent does not have any financial guarantee except to empty the holder's bank account!
Once patented you can manufacture or sell/licence your product, but if you get ripped off you have to take your own action. The Patent Certificate is only a piece of evidence.