I am the opinion that even if NHS will not pay for an eye test, there are firms such as 'Specsavers' who will give one for nothing; as a step towards a customer.
Having had an eye test, one doesn't have to purchase from the optician involved, but can request a prescription which can be dispensed elsewhere. There are small outlets in my area that are not opticians but can dispense a prescription and give one a considerable saving on a set of spectacles.
I know from experience....Ron.