Sorry for delay .... I have been away from the forum for a while.
I resolved it by removing the sort by option ....!
I can't really give you a link as I have removed the option, but the website in question (still in development) is here:
If you click on one of the categories you will see a Sort by (restyled) eg here:
If you then click on one of the brands eg Carl Hansen ... you will see the Sort By is there and it works.
However, if you go to Brands and select Carl Hansen ... you get the products listed but the sort by option didn't work here, so I removed it.
It may be something to do with the way I have everything set up .. as you can see there has been a lot of customisation ...