So it turns out that eating raw fish might not have been such a good idea after all

[Burney]

I will follow your advice either this Sunday or next Sunday if chicken wins the race for the nearest one

Please do not laugh but I have also tried rubbing a mixture of flour and mustard powder onto the fat layer at the start
Shall I just pepper it ?

No, that's OK (although I'm never sure how much flavour the mustard powder actually imparts, tbh). You should certainly salt and pepper it, though.

Have you a meat thermometer? If so, throw the ghastly thing away, since they lie and want you to cremate your meat.