jeez that’s £56 a tonne! 😯
But yeah, that’s the stuff.
Check your local builder’s merchant cant do a drop off cheaper – Travis Perkins, County, Bradfords, Wickes etc. Maybe do a rough volume calc as well to check that one bag is enough and that it wouldnt make more sense to get 2+ tonnes of loose delivered on a small tipper from a local material’s supplier (2 tonnes per cubic metre btw) – my local guy will do Type 1 for about £30 inc VAT a tonne loose 4 tonnes.
Id still go for whacker plate as its got a smaller foot for getting into your hole for when whacking lower levels. Dont forget to cut a decent vertical edge with a pick and shovel and to make sure you get a good mix of fat and fine agg in the hole.