Thanks for your question - I am Sam and I am one of the UK tax experts here on Just Answer.
HMRC hold a list of those companies for which the shares are accepted as holding a negligible value, of which this one is NOT listed.
Link for the up to date list here
However, HMRC are always willing to consider other companies, and you will need to write to them to ask them to consider this company, and whether the shares can be considered as one that fits the remit.
OR you can simply enter them on your self assessment tax return and include a note for the case to be referred to Shares and Assets Valuation Office.
I recommend that you write rather then just make a claim on your self assessment- because at least your letter will be dealt with in a timely fashion, for your self assessment to then be submitted accurately.
Their contact details are
Shares and Assets Valuation written enquiries
PO Box 38
Castle Meadow Road
Their telephone number is XXXXX(NNN) NNN-NNNNand they are open
8.00 am to 4.00 pm Monday to Friday
Closed weekends and bank holidays
But they will not be able to give you a ruling on these shares over the telephone, a written application would still need to be made.