Your numbers are off again, and you’ve based the figures on the way most people buy a primary residence, not how a property investor would buy a rental property. Also, not sure why you keep using the media headline rate of 6%….
There are still currently plenty of BTL mortgage rates at around 3-4% available and on an interest only basis, that £400k flat with a rent of £1400pcm is still a viable rental.
£400k purchase
£150k deposit
Interest only at 3.39% fixed for 5 years.
£706 per month.
Rent £1400 = ~£700 profit (subject to tax and the wonderfully convoluted “landlord levy”)
ETA - This mortgage, and many others currently available are variable or tracker, meaning that if the BofE base rate goes up, so will your mortgage rate, but…..if it comes down, your interest payment will do too. I expect interest rates to peak soon, as the UK won’t be able to afford it’s own debt repayment bill if they keep putting rates up, so I’d expect the mortgage repayments to go down over the 5 year term, not up.