I’ve just read on the BBC website that allotments are considered to be safe places to go as they are organised so that people are separated from each other. So you just need to ensure that you stick to the two meters rule if someone else is on the allotment at the same time as you. Sounds like an activity that will help with both mental and physical health to me. Enjoy!
Welcome to the forums @Joannebburn. From what I read in the Guardian today Michael Gove has suggested that working in allotments is acceptable so long as you keep 2 metres away from everyone else. The advice is changing all the time though, so it may be prudent to consult your local authority website on their policy on allotments.
Sorry that is a bit vague, it is so hard at the moment and important to keep yourself and your father engaged.