Tested positive for covid for the first time yesterday and had a shift this morning, I messaged my manager saying that I had tested positive and was not feeling well enough to make my shift in the morning. He told me that there were no longer covid restrictions for working so I could “come into work no problem” he then followed this up saying that I could ask to swap shifts with the only other guy who physically could cover my shift. This morning I still wasn’t feeling any better but the guy who could have covered my shift wasn’t picking up so I called my manager and he said that it wasn’t his responsibility to find cover as he couldn’t sort cover for everyone and if I couldn’t find cover I would have to come in. I live in the UK, was he justified in saying this?