I've found a solution to this which is a bit of a dirty fix, however it works and thats all that matters.

Linda McGrath (Ajeh) has also been helping me with this so credit to her.

See this thread about a mass products duplication tool she has been developing, works a treat.

http://www.zen-cart.com/forum/showth...=180447&page=1

So what I did was download this tool and install it firstly.

Then I moved my first class and track and trace categories to a category which is switched off called Chemicals Admin Category. First Class and Track and Trace are switched on inside this category as are all the products listed inside them. Then all products listed inside my Chemicals Admin Category have been duplicated to another category called Chemicals (the category where the products should all display. This means that all the products inside my First Class and Track and Trace categories are now mixed in the same category but when I put them through the cart it selects the correct postage method for the product in the cart. This is because my shipping/table1.php (first class) has code in it telling the cart to switch off first class if a Track and Trace item is added to the cart.

Bit of a dirty fix but it works.