Banco Santander (LSE:BNC) will increase all of its residential and buy-to-let fixed-rate mortgages for new customers starting tomorrow.
Rates are expected to increase by as much as 0.34%, while selected fixed rates in its product transfer range will also rise.
Lewis Shaw, a mortgage expert, believes other lenders will follow Santander and up rates as a response to "volatile swap rates".
He implored house buyers of that remortgaging to sort out the process as quick as possible or risk being caught out by the new rates.
"This way, you'll hopefully not miss out on lower rates because once they're gone, they're gone," he added.
The FTSE 100 has trailed higher to around 7,737, up close to 9 points.