This would be grievance worthy I suspect, as Customer Delivery Drivers, part of your responsibilities are dynamic risk assessments, if the recommended but not actual speed limit is 20 but actual is 30, then you're well within your legal remit to go 30, I would make the point that the Lightfoot software is faulty and in the grievance put if this were to go before a judge it wouldn't be deemed as a good enough reason for dismissal due to the probability of faulty software that lightfoot has.