If i want to fix a mixer tap on my basin...? Is it difficult. I have a hot and a cold tap...

Is it difficult. I have a hot and a cold tap at the moment and want to convert it to mixer. I have just had a new sink fitted by the council but they wouldnt give us mixer taps. So how can we get it done? and how much would it cost? Is it a big job? I can easily buy a mixer tap but its just fiting it thats the prob.
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Answers:    if you buy the taps then its just a matter of fitting it, it should cost no more than ¡ê40.00, my other half is a plumber
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It's not difficult because your hot and cold feed go into the bottom of the mixer tap. If you can't do it yourself then someone with some plumbing knowledge could do it (try a friend before paying for a plumber) and it should only take about half an hour.
Remember hot feed is to the left - it's done like that as a standard for blind people. Just in case you sell the house to one!