Part of the problem is that there are a lot of rules and regulations regarding the employment of 14-year-olds. For example, it's illegal for anyone to employ you for more than 5 hours on a Saturday, or for more than 2 hours on a Sunday. Many employers only want people who can do a full day's work. There are additional problems relating to the need to get a permit from your local education authority and with insurance (which might not cover under-16s).
You can read all of the rules here:
http://www.direct.gov.uk/en/Parents/ParentsRig hts/DG_4002945
If you've really tried every possible employer in your area, the only alternative is self-employment. None of those awkward rules and regulations apply to running your own business. So what are you good at? Some young people run car-washing or ironing businesses, for example. Others offer gardening services. I've even taught a 14-year-old lad who was earning more than I was, through his freelance writing for computer magazines. So perhaps you can think of something that suits your talents?
Chris