Do I have to go to work, if public transport is my only way of getting there and I don’t think that’s safe?
The current government advice in England (but not Wales, Scotland or NI) is to ‘actively encourage’ a return to work for those who cannot work from home, while trying to avoid public transport and maintaining social distancing.
Employees are advised to avoid crowded public transport and either go by car, or by walking or bicycle.
In my opinion, if you cannot get to work any other way, avoiding public transport would seem to be a reasonable reason to stay away from work, especially when the government has advised against it. Don’t forget, though, this would be unpaid leave.
There is at least a risk that disciplining you for refusal to travel may result in you being able to make a successful employment tribunal claim. Discuss this with your boss, though, since it is not easy to make such a claim and it will take a long time to get to the employment tribunal.