Have to agree with most of the above. Having GCSEs only puts you towards the bottom end of the educational achievement spectrum, and in a employment market where companies can afford to be very choosey indeed that will be a very obvious and easy way to filter you out of the selection process. You'll be competing for jobs against people who tick ALL the boxes - what will you bring to the party?
To be more general, with the overall devaluation of qualifications I'd say a degree was the new baseline for most careers, and unless you are a future Branson or Sugar, having the bare minimum education isn't going to give you the best chances in life. The application form for Starbucks ask you what A-levels you have.