She was portrayed by Annabel Brooks.
According to Luke's Grandmother, every country in the world has witches. In each country there is a High Witch who serves as the leader of that country's witches. The universal leader of all the witches is the Grand High Witch.
The High witch of England
Being the the High Witch of England, Nicola exercises added privileges and responsibilities that the other witches of England can not partake in. She formally welcomes the Grand High Witch to the hotel before anyone else. She also reviews witch business the Grand High Witch over tea. At the beginning of the annual witch meeting, The Grand High Witch is seen ordering Nicola to sit in the front row, yelling, “Come along, Nicola, down in front!” At the banquet, Nicola has the privilege of sitting at head table, right next to the Grand High Witch.
Nicola meets her end at the banquet along with all the other witches, when she unknowingly ingests Formula 86 (A magical potion that turns individuals into mice). Although the Grand High Witch created Formula 86 in an attempt to destroy all the children of England, Luke manages to sneak the formula into the witches’ watercress soup. Nicola is seen as the first witch at the banquet to begin turning into a mouse (Not including the cook who was not at the banquet)