Boris Johnson needs to take lead from other countries more severely affected by the virus. Italy reacted too late and thus it's already spiraled out of control now. The UK's numbers are small in comparison, but are rapidly increasing. As Prime Minister, he has had plenty of time now to find to conclusions and make decisions about what needs to be done.
Nobody should be out of pocket because of this, and nobody should be profiting from it; those caught re-selling sanitising products for many times their normal price should be fined heavily. Workers should have the option to work from home where it is feasible, and if it's not feasible there should be many extra measures put in place to make the workplace safer -- face masks, hand sanitisers, gloves, additional cleaning of equipment, etc.
Regarding mass gatherings, there is no reason for Johnson to do anything different than the likes of Italy, France and now Ireland, etc. Ban any and all public gatherings of more than 100 people until further notice, and make a decision as to play games behind closed doors or call them off completely.
Hospitals need to be quickly provided with additional supplies, and if necessary visas should be fast-tracked to get in additional doctors and nurses from abroad.