just to make sure I have it correctly, you need to have 2 different shipping rules for 2 different product types:

product type A = £7 per product Type A item

product type B = £0.99 per product type B item

meaning that if you had 5 items in the cart, 2 where item type A and 3 where item type B, the total shipping should be:
7 + 7 + 0.99 + 0.99 + 0.99 = 16.97

If that is the case:

create a new column in the cart object named "itemType"

in the add to cart button behavior, set the itemType column to A or B depending on the item.

create a shipping rule for item Type A as:
Triggers:
"Number of items with a specific column value"
if the number items where "itemType" has a value of "A" is ">" a value of "0"

Calculation:
"Based on items with a specific value"
Total of "Quantity" where "itemType" has a value of "A" "times" "7"

the shipping rule for item type B will be similar:

Triggers:
"Number of items with a specific column value"
if the number items where "itemType" has a value of "B" is ">" a value of "0"

Calculation:
"Based on items with a specific value"
Total of "Quantity" where "itemType" has a value of "B" "times" "0.99"