Enclosed is your reward cheque
Just imagine it:
"Dear person who recoverered our embarrasing lost data and saved our skins; enclosed is the monetary reward we promised":
A cheque for £8,670
That's £20,000 minus 40% PAYE,
Minus NIC employers and employee's contributions (we have classified you as an employee for tax purposes as you were essentially working for us in finding the missing data)
Minus CGT - as you didn't really do much work in finding the disks, plus the asset concerned was someone else's intellectual property upon which you have profited by reselling it back to the original owners.
Minus 17.5% VAT; we have taken the liberty of registering you for VAT, in case you fancy having a go at recovering all the other personal data we've lost; which would put your turnover over the VAT registration threshold.
Total deductions: £11,330. Total takehome: £8,670
Kind regards and thanks again.