It's up to you how safe you want your environment to be. You don't have to debate that with your landlord or anyone else. Your desires seem quite reasonable, given there's a WORLDWIDE pandemic underway and 100,000 dead in UK with many more injured permanently. Why not say explicitly to the landlord what you want and ask him to oblige with that chap or find another chap. If the allocated workman won't comply that should be the landlord's problem, not yours.