[ic] URL decoding problem

[DB]

I have a scratch variable named return_url which contains this string in
a 5.6.3 catalog:

http%3A%2F%2Fdomain.com%2Ftest.html

this does not work as a link. I want to change it so that it will.

I have tried:
[filter decode_entities][scratch return_url][/filter]
[filter op="urldecode"][scratch return_url][/filter]
[filter urldecode][scratch return_url][/filter]

but none of these seems to have any effect. Am I missing something?

DB