I'm not sure if you can mandate compulsory vaccination without being accused of infringing human rights.
What is this vaccination for?
Are people likely to already have been vaccinated previously? - Could they, for example, show you evidence of this?
Is there a simple test to show whether someone already has immunity to this particular pathogen?
What about any employee whose immune system is already compromised (for example, a cancer sufferer) for whom the vaccination might pose a risk?

You can state that the vaccination is a requirement by the NHS and those without it may be unable to do their job fully; and of course as an employer you can take steps when someone is unable to fulfill the entirety of their role. However, I'm not convinced you can make it compulsory.

In reply to Anna:

Thank you Anna for your feedback - the vaccination is for Hep B and some staff have already been vaccinated previously, although some high risk roles haven't identified those who have been previously vaccinated. I believe there is an immunity test that can be undertaken before the vaccination is administered. There are guidelines on the HSE website however, as an employer we have to take appropriate measures to protect our staff from the risk of infection. I'm just not sure what measures we can take bearing in mind that we have a number of staff who are already protected.

In reply to Raie:

Hi Raie
It looks that capability of undertaking work in these locations is contingent on them being vaccinated against Hep B. If there no other sites where staff can work it seems that dismissal for capability reasons is an appropriate course of action.

In reply to Ray:

Thank you for your comments Ray.

Hi Raie, we have a vaccination policy in my organisation. We are required to have one in law as we run GP surgeries (see link www.cqc.org.uk/.../nigels-surgery-37-immunisation-healthcare-staff).
In essence the policy states that we will pay for vaccinations and make sure employees have access to them (eg paid time off work to get them done). We don’t make it compulsory because people may not be able to have the vaccination due to heath or religious or other beliefs. Therefore we only strongly recommend that they are vaccinated, stay up to date with them and advise them on what vaccinations they should have. If someone is unable to get vaccinated then we modify their job if it is due to health or religion etc to ensure our practice/criterion etc isn’t inadvertently discriminatory. Eg hep B, despite being vaccinated, it doesn’t always work for some people therefore they don’t ever get immunity and so they can’t do bloods or minor surgery.
For example wording there are many nhs trust policies on the web that you can get inspiration from to suit your needs.

Hi Raie
It may seem like semantics, but I think Anna, Ray and Katy have the right approach. You can tell people that they must be able to demonstrate that the are protected against Hep B infection to work in an area but unless you are a doctor you can’t prescribe it.