About showing it, here's a quote from the IPO (it's a great website):
"By far the most common mistake made by people new to the world of patents is to reveal their invention too early.
If you reveal your invention in any way – by word of mouth, demonstration, avertisement, article in a journal or any other way – before you apply for a patent, you are making your invention public. This could mean that you lose the possibility of being granted a patent." (emphasis mine).
There is a guide of people to talk to as well.
As noted, it would protect you in the UK only. If a Chinese firm chose to make it, you could stop the import of it. If you had patents in every country you can stop them making it. Given enough money for lawyers. Witness Apple and Sam Sung at the moment over tablets.
I have no idea what your invention is, but I know it must be non-obvious, and contain an "inventive step".
As others have noted, a registered design (think marmite jar, for example) may be a useful protection. It's cheaper, and may be more applicable if you can't pass the "inventive step" test.
Have a look on the website - it is really good, clear and well written. Don't dash your dreams on the rocks!