Not wishing to put you off you have a hard task ahead of you.
Anyone investing who has a clue about investing will not be over interested in the technical aspects of your idea initially. They will be looking at whether it will make money or not as any investment they make will need to be repaid with a profit to their investors.
At the VC end they will be looking for lending large sums of money as their overheads are the same whether they lend 500k or 10m. Less than this you are looking at Angels or a company that would benefit and might invest. Angels are hard to find and usually involve third parties who will charge you for introductions but give no guarantees (beware of these and avoid like poison).
You will need to write a business plan (plenty of templates on line) 20 pages or so and also show the cash flow and the potential earnings. Everyone agrees that this plan is pure fantasy and that is of little use but everyone writes one and requires one so go with the flow.
Going back to the start explaining that you tool is the fastest recursive-descent compiler ever built and is based on Laplace transformations with Eigen values thrown in will have them running away screaming. Telling them that you have a software product that would used by 20% for the fortune 500 companies, sells for £500 pounds and is 30% faster and 50% cheaper than current competitors and that you have the IP on it and can patent it and that you have all the researched facts and figures in you business plan might lead to them having a further conversation with you at a deeper level to see what you have.
Any investor will be looking for you to put money into the project. Just adding your value by working evenings and then attaching a notional hourly rate to say you have put £100,000 in is not going to impress them. Asking for £100,000 for your wages for the next year is not going to impress them either.
Also you will also need an exit plan. Investors are not necessarily looking for a long term business but if they can piss Google of with the product enough for Google to buy them out at a healthy profit.
A working product/prototype with customer's/beta-testers will go a long way in helping.
Getting in front of the investors is the hardest part. Join Linkedin and other social networks to track people down. Write your business plan and send it to everyone you can think of that might invest. Read TechCrunch as they do events for investors and you might get someone there to champion you.
Mentors are good if you can find someone who will give you advice and help and contacts (hard to find).
There is more mush more but it boils down being able to sell to someone the idea and how it will make money not the tech innovation that you are adding.
Yes some people seem to be overnight successes' but then some people win the lottery with one ticket. Going down this route is hard and frustrating and will soak up your spare time and put friends of you for life but on the other hand you might just make a fortune and either way you will learn a lot on the way.
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Here is a link i found useful UK BUsiness Link
What can be useful is a number of different pitches that vary from 30 seconds upwards to a full 10 minute presentation that you can use in different situations. The "Elevator Pitch" is the one that you use when you get in at the 20th Floor, then Steve Jobs gets in at the 18th and you realise you can pitch to him and he cannot do anything about it. In that time you are obviously not going to explain anything technical or the mechanics of what you are doing it is just the essence of the idea. This by the way is NOT easy and while the 20 page plan + spread sheet is really hard work it will make you think about all aspects of what you are doing and will highlight the areas where you don't know what you are doing so you can get help.
You won't get it right first time so practise it to yourself in the mirror, your friends and family, my cat was a great listener to my stuff.