I have a half share in a property that I have never lived in,

Hello, I am Keith, one of the experts on Just Answer, and happy to help you with your question.
You will be liable to Capital Gains Tax (CGT) on the gain you make on disposal. This gain is calculated as follows. Take the current market value less the selling costs to derive a selling price. To calculate the acquisition price take the purchase price add purchase costs including stamp duty, add improvements (eg installation of double glazing, central heating extensions etc, but not routine maintenance which is allowable against rental income). Take one from the other and the difference is the gain subject to CGT which will, after deducting the individual's Annual Exempt Amount (AEA) of 11.1K will be taxed at 18% or 28% or a combination of the two rates depending on your income including the gain in the year of sale.
A worst case scenario would be a tax bill of:
200K - 80K = 120 / 2 = 60 - 11.1K = 48.5K @ 28% = say 14K of tax due.
But soft, if the property was let out than you would be entitled to Lettings Allowance of up to 40K instead of your AEA which could reduce the liability. If the property was let out as Furnished Property Rentals then you might be entitled to Entrepreneurs' Allowance which would limit CGT to a flat rate of 10%.
HMRC will insist on the current market value being used for the computation irrespective of the moneys actually received. If necessary HMRC will consult the District Valuer Services, part of the Valuation Office Agency who can provide current values if required. The Agency is a little known part of the HMRC empire and also responsible for rating and Council Tax assessment levels.
HMRC are likely to regard the scheme you suggest as not merely tax avoidance (legal), but tax evasion (a crime). I cannot recommend such a process.
I am so sorry to have to rain on your parade.