Hi there Francois, welcome aboard.

As you've seen, the latest UKBA requirement is to have a TB certificate as part of the visa application process.

Since you already have your visa there's no UKBA requirement for you to have one.

However, you may find the immigration officer at UK entry will ask you for an X-ray.
If you don't have you may be invited to have one at the airport. Depends on the airport.