TBH- I should hope the majority on the list would already be well aware that they are high risk and should isolate anyways:

• Those with organ transplants
• severe lung conditions like cystic fibrosis

From .Gov

Solid organ transplant recipients
People with specific cancers
People with cancer who are undergoing active chemotherapy or radical radiotherapy for lung cancer
People with cancers of the blood or bone marrow such as leukaemia, lymphoma or myeloma who are at any stage of treatment
People having immunotherapy or other continuing antibody treatments for cancer
People having other targeted cancer treatments which can affect the immune system, such as protein kinase inhibitors or PARP inhibitors
.People who have had bone marrow or stem cell transplants in the last 6 months, or who are still taking immunosuppression drugs.
People with severe respiratory conditions including all cystic fibrosis, severe asthma and severe COPD
People with rare diseases and inborn errors of metabolism that significantly increase the risk of infections (such as SCID, homozygous sickle cell disease
)People on immunosuppression therapiessufficientto significantly increase risk of infection
Women who are pregnantand who also havesignificant heart disease, congenital or acquired