Learn on the job by actually doing the job.
Many of the larger companies have recruitment schemes where they look for the brightest school leavers to train up on their own internal training schemes. This wouldn't necessarily result in a qualification but you will get a wage and might be also be fast-tracked for promotion within the company.
Have a look at the work experience opportunities listed in this section in different industry sectors. Once you have tracked down your ideal position, it's a case of going for it and applying.