UK Employment Law

Scenario
Until recently, David Jeroy was a machine operator at Kitchen Planner (KP). He was employed building custom kitchens in the joinery shop on regular, repeating, temporary, fixed term contracts, each of which lasted three months. There was sometimes a gap of approximately one month between contracts and, on one occasion, a gap of 6 weeks. This was as a result of varying work-loads in the joinery shop, dependent upon the number of orders that had been received. In total, David has worked for KP for three and a half years.
Two months ago, when arriving at work one morning, David told his supervisor, Chris King, that he had just won £25,000 on a lottery scratch card and that he was going to go out celebrating at lunch-time and book a great holiday for himself and his family. That lunchtime David was late back from his meal break. Chris noticed that David was laughing and joking very loudly with everyone and Chris thought he could smell alcohol on him. Chris quickly called two security staff, who escorted David to the office of Mary Kerry, the Health and Safety Manager. Chris told Mary that he thought David had been to the pub and had been drinking. Mary told David that coming to work under the influence of alcohol was completely unacceptable as the wood-working machines he used could be dangerous if operated without due care and attention. David vehemently denied drinking alcohol and said the smell on his overall came from a cleaning product that he had spilt when he was cleaning his tools. Chris asserted that he knew that David had been celebrating his lottery win at lunchtime and he suspected that he had done so in the local pub; Mary decided she could not take a safety risk – he could not be allowed to operate machinery when he was suspected of being intoxicated and she said he would not be allowed to work in the joinery shop again. She said that he was summarily dismissed and he should leave the premises immediately.
It is now two months since David left KP. The company has received an ET1 claim form today stating that he was claiming unfair dismissal and wrongful dismissal and you have the ET3 response form to complete.
Task: Give your advice as to the legal issues involved and the strength and/or weaknesses of the company’s case. What do you need to do to either refute the claims of unfair (is David Jeroy entitled to claim an unfair dismissal regarding the criteria that he should be an employee and have a minimum of 2 years continuous employment) and wrongful dismissal at the Employment Tribunal or, if you believe the company’s case to be weak, what you should do now to prevent the case going to Employment Tribunal?