M9 Getting URL parameters in server side script

I am trying to pass a variable into an admin form along with the URL, is there anyway to retrieve this in a server side visual script and assign it to a Local variable?

I have read ways of doing it on the client side and posting it back but was wondering if there was a cleaner way to do it server side?

HttpContext.Current always appears to be null no matter where I run the code (tried it on form load, on a button press, etc) suggesting that the code maybe running under a serperate thread to where the page is handled.

Any ideas / alternatives people have would be a great help!

Thanks,

David