wrote...
....
The MonthSales named formula is defined as follows:

WorksheetName=RIGHT(CELL("filename"),
LEN(CELL("filename"))-FIND("]",CELL("filename")))

Do you mean WorksheetName is defined as above?

What does the cell formula

="["&WorksheetName&"]"

return?

MonthSales==VLOOKUP(INDIRECT(WorksheetName&"!$A "
&2+ROW()+2),London!data,2,FALSE)

Why 2+ROW()+2 rather than ROW()+4?