That's the whole point though at risk is something which MAY lead to a situation which MAY become a risk to life or property, you cannot stop a customer using that appliance if they want to, merely arm them with the information to make a decision.I can quote from viper:
'Under the guidance of the gas safety installation and use regulations, there is no legal requirement to disconnect an at risk installation or appliance'
and:
'The customer's permission must be sought to either rectify the appliance / installation or turn the appliance OFF'
However a common sense caveat is also included at the end:
'Gas installers must always err on the side of safety'