In a nutshell:
If it's your only property, you won't pay any tax on any profit made, although you may have to declare it as your place of residence - not too sure on this to be honest :(
If you own other properties (including your own home), then you're allowed a certain amount of profit before you pay tax. This allowance is your capital gains tax allowance and I think it's £11k for the tax year 2014 -2015.
So, if for example, you pay £60k for a house, spend £15k renovating it and then sell it for £100k - your total profit is £25k. You'll pay tax on £14k of this - the rate you pay will depend on whether you're a high rate tax payer or not.
See:
http://www.hmrc.gov.uk/cgt/intro/basics.htm