glloyd, I really wish you the best. Two years is a long time so you are obviously dedicated. All I can do is explain where I think you are and what options you may have. Firstly Big and medium size companies train their own people, normally from 16/17 yrs on formal apprentice contracts. It takes 3-4 years, half of which is college the other half site work. So at 21 years they have qualified electricians who have the experience to do the work. You have the qualifications but not the experience. Applying to them is unlikely to get you anywhere, as even if they wanted to they could not take you on to do Free work to gain experience, it is against the law owing to National Minimum Wage regulations. Hence the lack of response from them.
dcelectrical's advice is good. If it experience that you are after then sole tradesmen are a better bet than big companies. So take his advice and try that route. Your only option with the larger companies to is to try for an Adult Traineeship, but they are like gold dust.
Englishman is not wrong you need contacts, electricians to be specific, who could provide you with the experience you need. If I were you that is where I would focus.
The one other possibility with the large companies is that you live in a region where there is government funding for adult trainees. Your local employment centre should be able to advise you on that. Basically if you qualify a large company may take you because they are entitled to claim a grant for your training. It is worth asking.
I wish you all the luck you deserve and let us know how you get on.