Previously, the applications had to be made separately and with brokers waiting for a case to finish before the other could be started.
It also means landlords will not be tied into a rate switch should the further advance request be unsuccessful.
Under the changes, applicants can secure one of TMW’s current switcher products and complete on the further borrowing within six months.
Landlords on reversionary rate mortgages could also be able to borrow more as they are subject to the standard affordability assessment.
Ian Andrew, director of intermediary relationships at Nationwide Building Society (pictured), said: “We are continually looking at ways to both streamline and enhance our processes to ensure applications are as quick and easy as possible for both intermediaries and landlords.
“These changes, which will save time and open up a wider range of options, are the latest in a line of improvements we’ve made to support the broker community, including the enhancements to TMW Online last year and subsequent improvements to case tracking.”