actually, BRCGSV8 allows it as an exception:
7.2.1 (Interpretation guide): • jewellery must not be worn apart from plain wedding rings or wristbands (i.e. without stones that may fall out). Exceptions must be minimal and must not constitute a risk to product (e.g. wrist bands identifying a particular medical condition, such as epilepsy or an allergy, may be worn where product is not at risk of contamination). Where religious reasons prevent the removal of an item of jewellery, then it must be covered and the site must complete a risk assessment to confirm how this will be achieved (e.g. by totally covering the item with the wearer’s clothing, or by wearing overalls that are buoned up to cover the item)
but also pls see that it shall be cotrolled:
"The requirements must be communicated to all personnel (e.g. through induction training and sign-in procedures for visitors and contractors). Consideration must be given to staff who are not native speakers and appropriate methods of training (e.g. use of translators) must be provided for them. Compliance with requirements must be checked regularly, for example by incorporating checks into daily or weekly good manufacturing practice audits, or through the questioning of personnel at regular intervals"