Lord and Prof titles Someone has a title Lord and is a Professor.  How will I address a letter?  And what will the correct manner be after Dear?
Looking at this link, Professions, as provided by erstwhile editor in the comments to your question, the answer would be Professor Lord [Such-and-such]:


  If a professor is also a member of the peerage, or a knight or dame, the academic style and title may be combined as ‘Professor Lord Ryder’ or ‘Professor Dame Elizabeth Pulteney’. He/she may prefer to be known by title alone.