So a few years ago, you could buy a house for £200k and invest £50k to become a landlord. The rent income could be used to pay off the remaining £150k equity with no tax implications.

Now you have to pay income tax on the income, albeit a few expenses/interest that are exempt. Losing 40% of your profit is a big hit to take. That's before the impact of increased interest rates. You can move to a limited company but that costs a small fortune in stamp duty. The two choices are increase rent to cover some of the shortfall or sell up and put your investment into a lucrative place such as SP500 and pull back c.8-10% pa.

My actual example is I invested £70k into a flat worth £230k. I charge £1050 rent (going rate is £1200 but I'm not an asshole landlord) My mortgage at 1.8% is £270p/m I pull £650 profit per month before tax. When I remortgage with higher rates, my profit will be £200pm before tax. That's £5.4k I'm worse off per year pre tax. I have to ask myself, is £70k investment worth £120 return per month? Probably not and I could probably do better in a S&S ISA. I could go and clean houses/offices once a week for 2hrs to make that £120. My tenant is a good person, a key worker and I don't see why she should be punished with increased rent to make up my shortfall.
Selling suddenly doesn't seem that bad of an idea!! Plus no tenant headaches.