Absolutely correct - cant really do single pilot in small cabs eg rotary either
However, the reality is that the Treasury will overrule the Departments of Health as otherwise there will be a massive hit to the economy. They are already trying not to use the word 'exit', fearful that the British public are not as stupid as they are assumed to be by politicians and may refuse to 'exit' lockdown and risk another 300,000 deaths.
So it is likely the 2M rule will go quite early. The question is how much risk the instructor and pilot wish to take.......in fairness in small aircraft the airflow minimises the risk of infection. Over on Rotorheads there is a thread running with advice for PPE in EMS work. So IMHO it is likely it will not be illegal to train. Whether you want to take the risk is going to be a personal matter heavily influenced by your financial situation