Gaggia Hose Clamp ø 7.8-9.5mm - 996530007742  £1.32

If you don't have a special tool for these clamps (I expect there is one), you can use carpenters pincers instead. Put the clamp on the hose, push the hose and clamp onto the pipe, squeeze the clamp's rectangular projection at the base hard with the pincers to close it up. It won't be quite as tidy as the proper method but it works pretty well.