Daniel, as mentioned before, what do you have on grandmother Iris?
Have you got grandparents' marriage cert from 1939 to at least confirm her father's name?
Given the location of Maurice's death that Rosie mentioned earlier in Hillingdon, there is a death of an Iris Herbert, b. 1917, in the area of Barnet in 2001 (reg. January). Do you know when and where Iris died? Do you remember her birth day date? This death entry shows a birth of 18 June 1917.
Monica