Assuming it is an un-amended contract, you would have to be able to demonstrate that the consultant did not, to quote clause 21.2 "use the skill and care normally used by professionals providing similar services to the services".
While it is on the balance of probability, note that you are the one who has to demonstrate this by producing evidence sufficient to sway the argument against any counter-evidence they produce.
While it is on the balance of probability, note that you are the one who has to demonstrate this by producing evidence sufficient to sway the argument against any counter-evidence they produce.