Thanks for your explanation Ian. I was not aware that I needed to include the amount in both 6 & 7 (mainly because the VAT return clearly states that box 6 is sales and when reading up on the reverse charge instructions I had not seen anything to advise that my purchases needed to be added to the sales box too).
I really wish that HMRC would issue clear, simple instructions for VAT returns that everyone adheres to. I was advised at a VAT inspection that I should have been including all of our sales to the US in box 6, which I had not been doing as AFAIK sales to the US are out of scope of UK VAT. I now see that QF excludes sales to the US in box 6 so presumably the VAT inspection lady gave me the wrong information. I did ask for clarification in writing (along with other enquiries), however they didn’t bother to include that in their reply (presumably because they didn’t want to admit that she was wrong).