excel+training+london - Copy / Paste Number Format

Sometimes when I copy and past a column of numbers to another column the clipboard icon appears and i can click on it and select "convert text to numbers" or something like that. I want to do this, but Excel only asks sometimes! How do i get it to ask, or is these another way to convert text to number (ie so the string of numbers goes from right aligned to left aligned to show its a number)

I dont think just doing format "number" will work as these are NI numbers, not actual numbers.

I'm doing this to use the numbers in an index match formula as it wont recognise the match if it thinks the numbers are text.

Thanks

Jen