We've always been quite bullish on this, you are encouraged to spend your sports premium on anything that improved the health and wellbeing on your school's community - especially when allocating a proporiton to promote healthy eating and learning (ie. lunchtimes).
See the below shots from From the DfE's Creating a culture and ethos of healthy eating where it clearly states that:
Using premium spending to promote healthy eating and learning, including breakfast and after school clubs
We have only heard of schools have their SSP taken off them for NOT spending the allocation, and you are encouraged to utilise spending on innonative projects including the Better Lunchtimes Project.
We've in fact, had schools praised for prioritising lunchtimes and improving the behaviour and welfare of their children in doing so.
Ofsted’s new Common Inspection Framework includes a judgment on personal development, behaviour and welfare.
As part of reaching this judgment, throughout their entire inspection, inspectors will look at the extent to which schools are successfully supporting pupils to:
make informed choices about healthy eating, and fitness
gain knowledge of how to keep themselves healthy
If your lunchtimes are NOT where you'd like them to be, an proportion of your SSP being allocated to prioritising them is encouraged.