Thank you,

I had worked out that Row_Number could help me and did something nearly exactly the same

(ROW_NUMBER() OVER (PARTITION BY a.Col1 ORDER BY a.Col2 DESC)-1) / 25

Only I have -1...

I am actually looking to do something slightly different, I want to number data returned in a query the first 25 row would be numbered 1 the second 25 numbered...