Should I cancel my overdraft?

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I've just taken out a £3500 loan to pay off my overdraft and credit card. I've already managed to pay off £2000 of other cards and credit agreements I had in the last 6 months. I'm planning on applying for a mortgage eventually once I've saved enough for a deposit. I'm wondering if I should cancel my overdraft now that it's clear? I remember hearing somewhere that having available, unused credit looks better on your credit file? So from a creditors perspective, would it look better to leave it in effect or cancel it? (I wont be tempted to dip into it, the debt was accrued a long time ago when I was young and silly.)

Should I cancel my overdraft?