Use of ampersands in name value pairs of a url

Hi all,

I hope I'm not missing something obvious here...

I'm generating a url for the source of an image of the form:

<img src="http://123.456.0.1?doc=myimage.gif%26instance=1"/>

Now the problem is that the escaped ampersand '%26' is not being
interpreted as the delimeter for the name value pairs, and doc is coming
through as 'image.gif&instance=1'.

The only way around this I can see is to use &_amp; in the stylesheet
with disable-output-escaping - but there must be another way?

How can I build a set of name-value pairs in the stylesheet that don't
require d-o-e?

thanks
andrew