I'd advise you do a very detailed balance sheet which includes impact of recent tax changes (which are explicitly designed to financially discourage further investment in BTL).
Compare benefits with new pension rules of your aim is to fund retirement...
And most importantly, research your area. There are several areas of London where if you'd entered BTL summer 2014 or so....well you'd be crying already...capital values down, income reduced by tax changes and a glut of new build 2 bed flats coming on the market over the next 24 months. Stamp duty and increasing strength of sterling are not just biting the prime segment; effects are distributed down to about 700k price point.
Wage growth figures and general economic data just out tell a more accurate picture of tenants ability to pay than usual Tory hype, that's for sure. On the upside, maybe interest rates will stay low for longer, based on that.
In summary, BTL is not the meal ticket it used to be by any means. A thoroughly researched financial analysis is required to determine whether it's right for you, based on your funds, life objectives and area of investment interest.
P.s. am ex btl landlord, did v well out of it, but the numbers just don't add up any more for London in my area of interest (zone 1)...Good luck!