It was late when I posted, sorry for the confusion
I have found the answer now, may help others.

The original data is in cells A1-KG3 (3 long rows). The info to be added takes up two columns, and so I needed an empty column inserted between each column to allow for this.
So original data would be in cells A1, B1, C1, D1.....KF1, KF2 and repeated in rows 2 and 3.
What I needed was data in A1, then an empty column, data in C1, empty column, data in D1, and so on.
The solution was to put a new row in below the data (say row 6) and put ascending numbers in ths (1, 2, 3, 4, etc) to the end of the row. then copy this and paste it and the end of the row, so I ended up with this

A1 B1 C2 D1...KF1... KG1 KH1, KH2, KH3, KH4 etc

1 2 3 4 656 657 1 2 3 4

Then do a sort "smallest to largest" on the new row, which ends up as

A1 B1 C1 D1 E1 F1......

1 1 2 2 3 3
(data) (empty) (data) (empty) (data) (empty)

Not my solution (thanks youtube), but a very handy one indeed.