I've got a form from Credit Suisse to return which has come with I assume is a pre paid envelope (Nicht Frankieren)

Is this ok to use from the UK?

Unless they specifically sent it to the UK, it is probably only for Switzerland...

They've specifically sent it to me at my address in the UK!

But I know what you mean

Hence the question

There are such things but this sounds rather like a mistake. It must have written on in international business reply in which case it is valid oh and they are only valid outside of the country you are sending to...

I'm pretty sure you're right. I'm gonna whack on a stamp for safety's sake.

That's a lot harder to do than it used to be. Gone are the days i could look up the rate to a certain country and plonk the appropriate value of stamps on a letter. Now I think I have to assess how large the letter is...and as for getting the value of stamps... "Sorry sir, we only sell books of first or second class stamps"

I imagine that if you go into your local post office (assuming it hasn't been shut down in the latest round of cost cutting), they'll be able to advise you how much you need to pay. I am of course assuming you are in UK at the moment. Maybe I assume too much