This is most probably happening because you are using multiple locations. Shopify calculates shipping for items in cart from different locations separately and adds up the shipping rate. In your screenshot, the two items are most probably from different locations, and hence the shipping price is £4.99 + £4.99 = £9.98.
This is a long standing unsolved problem in Shopify as evident from this thread.
We have developed a solution for this problem in our app ShipMagic. If you wish to give it a try, you can install the app and reach out to live chat support for more help on how to set up the app for this.
If you have only configured a general shipping profile and all the products originate from a single inventory location, then this shouldn’t have happened. You may need to reach out to Shopify support
I see there is a 14 day free trial - can I assume that during that time I can set up and test the profile to ensure the customer is only charged once for orders under £40. After that 14 day period its £9.99 per month?