"Corporate tax" is a generic, international term for a tax or taxes on the capital and/or profits of companies or corporations (as they are known in the US). "Corporation tax" is the specific name for the tax levied on the taxable profits of limited companies and some other types of organisation in the United Kingdom.

So the expression "corporate tax" can be used in the UK in a general sense to refer to tax issues affecting companies, as in "corporate tax structure" or "corporate tax reform", for example, but the specific UK tax will be called "corporation tax".

"Corporation Tax is a tax on the taxable profits of limited companies and other organisations including clubs, societies, associations and other unincorporated bodies."
http://www.hmrc.gov.uk/ct/getting-started/intro.htm

"Part 2A sets out proposals to reform the UK's CFC rules on the key issues of monetary assets and intellectual property. Corporate Tax Reform Part 2A"
http://www.hm-treasury.gov.uk/corporate_tax_reform.htm


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Note added at 1 hr (2012-02-06 11:42:26 GMT)
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My answer is loosely phrased: I really meant to say "UK tax on the profits of companies and some other organisations".