I am writing to you regarding my son, [name], who is scheduled to have a cataract operation at your hospital on [date].
My son is just [under ten] years old, and therefore, as you can imagine, feels some considerable level of trepidation and anxiety about this procedure, which I am keen to mitigate for him as much as possible, particularly considering the deeply harrowing and traumatic ordeal he has already undergone in his short life.
In [year], aged just [under seven], my son was diagnosed with lymphoma, and therefore began a gruelling treatment schedule of chemotherapy. Although he was given the all-clear in [date], just weeks later, he became symptomatic again, and diagnostics revealed the cancer had returned.
We were offered the choice of more chemotherapy, radiotherapy, or an experimental drug treatment, which had not been widely utilised on children. It was an extremely difficult decision, but, keen to save our son the further invasive trauma of chemotherapy, we opted for the drug. We were delighted when [name] had a favourable response to this treatment, which was followed up by a bone marrow transplant in [date]. This was successful.
To our immeasurable relief, the cancer has not since returned, and we hope [name] will now be able to enjoy the rest of his childhood unencumbered with further serious illness or traumatic medical intervention - although he has developed both thyroid and growth disorders because of his ordeal, which he is currently receiving medication for.
Additionally, as a result of his chemotherapy, and as is common, [name] has developed bilateral cataracts, which require removal as a matter of urgency, for obvious reasons, including allowing him to properly focus on his schoolwork, which he is increasingly struggling to do as his vision continues to deteriorate.
Initially, his cataract procedure was scheduled for [date in 2020], but when I informed the hospital we did not wish [name] to receive a Covid-19 test prior to surgery, this appointment was cancelled.
Since that time, I have taken legal advice on this situation, which I am continuing to receive, and I have been advised that it is in breach of medical ethics law surrounding informed consent, and international human rights' treaties regarding coercion in medicine, to withhold surgery on this basis.
My right to decline Covid testing for my son is protected both by the Montgomery ruling , which informs the General Medical Council's guidelines on informed consent, and which all NHS surgical staff are bound by, as well as by UNESCO's Universal Declaration on Bioethics and Human Rights, which states at Article 6, Section 1:
"Any preventive, diagnostic and therapeutic medical intervention is only to be carried out with the prior, free and informed consent of the person concerned, based on adequate information. The consent should, where appropriate, be express and may be withdrawn by the person concerned at any time and for any reason without disadvantage or prejudice." 
In particular, I feel that the highly invasive nature of the nasal swab that is used for Covid testing is unnecessarily distressing and traumatic for a small child who has already endured an inordinate amount of medical trauma in his life.
Further, extensive evidence reveals that neither the PCR nor lateral flow tests are reliable indicators of infectious disease, and this has been detailed in many reputable publications and journals [see: 3, 4, 5, 6].
In addition, poor application of the swabs has been reported to cause severe damage to the delicate membranes at the top of the nasal cavity (7), whilst many test kits have been shown to be contaminated, due to inadequate quality controls (8).
Concludingly, I do not feel it is in my son's interests to receive a Covid test, and therefore I do not consent to his receiving one. I now seek your swift and urgent assurance that Covid testing will no longer be deemed a condition of [name]’s surgery, and he will be able to proceed with his urgently necessary cataract operation on [date], with no further expectation that he will undergo Covid testing,
I look forward to hearing from you.