If you have lived in the house, the time you gain relating to the proprtion of time spent living in the house is exempt from CGT.
Also, providing you have lived in the house at some time, the last 3 years of ownership are tax exempt also, regardless of the fact that you did not live in it during those years.
Plus, providing that you have lived in the house at some time in the past and you have let the house on a formal basis you will also qualify for "letting relief" which will further reduce your capital gain.
If you sell in 2006/2007 you will have an annual tax free gains allowance of £8,800 but this you cannot use earlier years unused allowances.
Improvement costs (new bathroom, re-roofing, new windows, total rewiring/replumbing etc) can be deducted in arriving at a net gain value as they should not be deducted from rental income, only repairs and renewals can be deducted from that income.
A) Have you ever lived in the house ?
B) Did you declare the rental income to the Inland Revenue ? (Will be dodgy claiming letting relief if the renatl income was not properly declred and subject to tax)