I had an email this morning informing me that I had an online message from HMRC so would I please log on to have a look at it. I did, and to my complete surprise they thought I owed them over £1300. This was news to me: it was all in penalties for not filing a tax return last year. Another part of their website has a questionnaire - that you can only see when you are logged in - which assesses whether you need to fill in a tax return or not. Mine says I don't. Furthermore, on my last tax return, submitted in January 2019, we stated that we had wound up our partnership on 31/8/2018.
I've just phoned HMRC and after a bit of a wait, all the penalties have been cancelled.