Hello, I am Keith, one of the experts on Just Answer and pleased to be able to help you with your question.
This would not be an HMRC approved share scheme. Here is the guidance from Saffery Champness Chartered Accountants:
'There is no income tax or National Insurance charge on the grant of an unapproved option. Income tax is, however, chargeable on the gain realised by the individual on the exercise of the option. If the shares are unquoted and the company is not an unquoted subsidiary of an unquoted parent, then there is generally no National Insurance on exercise and the income tax is payable via self-assessment as opposed to PAYE.'
Thus you are liable to Income Tax at your marginal rate of tax on the gain made between the acquisition price of these shares and their selling price. You will have to declare this on the appropriate annual self assessment tax return at the end of the relevant tax year.
By the way, in your position, are you claiming Tax Credits? It is possible that you are entitled to these. A trip to your local Citizens Advice Bureau might well bear fruit. They are very well up to speed in such matters.
I do hope that you have found my reply of assistance.