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Working 50 hours and wondering if its worth it?

Hi Guys,
Just wanted an opinion if I should be working lots of hours or if the tax that I pay will not be worth putting in the extra hours.
I am looking for an an apprenticeship at the moment and I have been contributing loads of hours into my part time job I had at college. Now I have kind of gone full time, however lots of my colleagues work 25-30 hours a week and I've been doing 45-50 (the same as the managers) and they keep saying that the "taxman" is going to love me, the question is it really worth doing as many hours as I can or is the tax I am going to have to pay outweighs the amount of work I am doing. e.g making marginal amount more than my colleagues.
Just want to hear some thoughts, Cheers