Over the past year, total business investment in the UK reached £198bn.
The cost of renting has increased by 33% over the past 10 years to £747.
Rental properties across the capital are empty for an average of 24 days.
The lender has also upped the maximum loan size on 80% LTV products to £2m, on 85% LTV offerings to £1.5m and on 90% LTV deals to £1m.
There were 29,490 of these mortgages recorded.
The RLA cited the 3% stamp duty levy on extra housing added in 2016 as slowing down investment in new rented property.
The growing number of landlords opting for shorter-term rates has been fuelled by the shorter early repayment charge periods.
Over a quarter (27%) of landlords experienced an increase in tenant demand during the final quarter of 2019.
In 2019 there were 2.66 million landlords in Great Britain, 8% fewer than the 2017 peak.