gcse's mean f**k all mate take no notice, my grades were not worth a wank, a went to college for nearly 5 years , the maths can get a bit hard, but if u stick in you will get through, a would advise going for and electrical apprenticeship, but a would say that cause thats what a did, plumming is a bit more of hard work, they work on guttering on house roofs etc, work with shitty toilets, oh yes a could go on if a want lol.
good luck a hope it works out