Do you mean first case in the UK ? And before the discussion was about the potential for immigrants or travellers to bring it in as it wasn't here before?
This is the first time I've seen it reported, so maybe it is the first example in the UK.
However, the reports online (BBC, Guardian etc) describe this as the first national alert for such a strain, and says the outbreak started in March. I wonder if there have been cases before which were not publicly reported as this has now been.