CGT reduced to 18% for gains made after 6 April 2008.

In essence, the gain is sale proceeds (or market value if you give it away) less the original cost.

Things like letting charges, mortgage interest etc get deducted from the rental income you receive in establishing whether you have any taxable rental income. This could be at 40% depending upon how much you earn.

Now for the caveat, this is a very simplistic overview so best go and see someone.

Regards

Jeff