MDPE Pipe

[ijp]

Hello all, I'm running some 25mm mdpe down my garden from the house, I know you have to go down 700mm to protect it from frost etc, but can this depth be reduced if I use something like this to insulate it https://www.screwfix.com/p/pipe-insulation-28-x-13mm-x-1m-35-pack/43273 if so would 500mm be ok?