I'm fairly sure that the rent received and insurance payments will be irrelevant in the working out of your capital gains, as these should have been declared every tax year as income and expenses. The interest on your mortgage repayments will also count towards expenses to offset against your rental income.
Your capital gains is the difference between the selling price and the total outlay for the property (buying price plus any costs incurred for renovations, etc).
For this coming tax year, the CGT allowance is £11 000 - any gains over that will be taxable at either 18% or 28%.
See:
http://www.hmrc.gov.uk/rates/cgt.htm
A solicitor will not sort this - you need an accountant, as The Builder suggested.