The short answer is no.
This is a common myth often perpetuated online due to a misunderstanding of the science, but current flu vaccines used annually in the UK, including this year, do not contain mercury or mercury-based preservatives.
A preservative called thimerosal which is mercury-based has often been used in the past in the manufacture of certain vaccines but this is not the toxic mercury we talk about that is known to accumulate in our food chain. Thimerosall was removed from UK vaccines between 2003 and 2005, and is no longer found in any of the childhood or adult vaccines routinely used in the UK.
Thimerosal is occasionally used in flu vaccines for outbreaks such as swine flu. We are always very transparent when this happens so that you can make an informed decision as to whether you would like to be vaccinated or not.
In conclusion: none of this year’s flu vaccines contain mercury-based preservatives.