In theory yes, but you also have to get a college to accept you for the extra year which they might not if you already have successfully completed another qualificatuon of the same level
Also there would be no point, yes it wouldnt cost you anything but it would waste your time, there is no point staying put at the same level in education, either leave and go to work or progress and do a higher level qualification i.e. University
Unless you want to dramatically change what you want to do, or there is a requirement for a specific few subjects there would be no point, also if this was the case yoy might as well just do a foundation year, it would be quicker and actually tailored to the degree programme that you would be studying, also you would get to go to uni sooner rather than wait another 2 years still studying with 16 year olds
Do you have any other career aspirations aside from IT?