Thank you for your support.
The position for your type of organisation is highly complex, but if you are not making supplies over the VAT threshold, currently 81K pa, there is no requirement to register. Here is the HMRC advice on the matter:
'If your turnover of VAT taxable goods and services supplied within the UK for the previous 12 months is more than the current registration threshold of £81,000, or you expect it to go over that figure in the next 30 days alone, you must register for VAT.'
Should there be any danger of the limit being breached I would urge you to consult HMRC as to your position. If you do not have to register either because you are below the limit or are advised by HMRC to the effect that registration is unnecessary you should endorse your invoice with a note that your organisation is not registered for VAT. Thus customers know where they stands in the transaction viz a viz their own VAT account.