Right up my street this one. Before you think about going down the road of patenting an idea or talking to potential investors you need to do quite a bit of legwork yourself. I'd suggest you do the following in this order:
Check on the internet and at the patents offices (UK and US) what's out there already. Use a range of searches to see what's similar as well as looking if there's something identical. Similar ideas often have very broad patents that may exclude a new idea even if it's not exactly the same thing.
Work out what can actually be patented (concepts can't, but new uses for modified existing things can)
Go through the exercise of doing a business plan covering sourcing materials, manufacture, distribution, personnel, start up capital and other financial requirements, equipment, market research and cost everything. Even if you don't intend to do it yourself, you need to have a good handle on what's required, have the knowledge to take into any production or equity negotiations you may have to undertake and have a strong case for raising any investment required. If the idea needs testing, think about building a prototype or the real deal and testing the shit out of it.
You'd have to finance everything up to this point yourself, so the more checking you do, the less money you'll waste if for any of a number of reasons it doesn't work out.
If you're still convinced it's a goer at this stage, then start thinking about protecting it before you talk to Banks, VCs, Angels or potential partners e.g. manufacturers. Obviously you'll have to tell them something so it's a balancing act between protection and sharing.
Going through this process may lead you to modifying your original idea as a result of information you uncover along the way, so apply all the checks and tests to any variation of the original idea - objectively.
Patenting can take up to 4 years but you have some limited protection once you've registered. Still need to be careful who you share the idea with, but once you're going down that road you'll need to move quickly.
As a general principle, do as much research and development as you can without committing much in the way of finance before you have to. The other main thing is to try to be objective throughout. I've worked with many innovators who are so in love with their ideas that they can't (or don't want to) see the obvious flaws. Always a good idea to get as many trusted people as possible to play the devil's advocate.