I can't believe your even asking.Why?
Surely building a bomb shelter in your back garden is pretty normal behaviour here.
Nice Anderson shelter by the way, @Martin Hocking It'll look great with a few vegetables growing on the sides. I might even build myself one, seems like the ideal place to hide from the Mrs next time she's on the warpath because I've trodden swarf into the carpet or sat on the sofa in dirty overalls.