For three years, mortgage porting in the UK was a fiction — every major lender quietly refused new ports, citing "operational capacity" while the back office shovelled applications into a discreet pile marked declined. In May 2026, that is changing. Three of the big six (Nationwide on 5 March, NatWest on 28 April, Santander on 10 May) have reopened porting for five-year fixed-rate residential mortgages, with the others expected before Q3 ends. If you fixed your rate at 1.7-2.4% in 2020-2021 and you have been quietly putting off a house move because the new SVR makes upgrading unaffordable, the maths just changed.
What porting actually means
Your existing rate moves to your new property, on the same outstanding balance, for the remainder of the fixed term. If you owe £180,000 at 1.85% with three years remaining, you can take that £180,000 and that rate to the new property. Anything you need to borrow on top — say, you are buying a £400,000 home and need to mortgage £300,000 total — is treated as additional borrowing at the lender's current rate (4.6% to 5.1% for most porting tiers as of mid-May 2026).
The trap that catches half of applicants
Affordability re-checks. Even though you are not borrowing more on the ported portion, every major UK lender re-runs full affordability on the combined balance — which means if your circumstances have weakened since 2021 (a redundancy in 2023, two children, a side income that has stopped), you can be declined even though you are not adding a single pound of leverage.
The way around this — for buyers in solid earnings — is the seven-day pre-approval written by the lender before you make an offer, which is now a standard product at Nationwide and HSBC. If you sit between £55k-£85k household income with no recent credit events, the pre-approval almost always clears within 72 hours. Above £85k, it is automatic. Below £45k, it is currently being declined at about 35% of applications even with a clean file.
The new "blended rate" disclosure
From 1 March 2026, every lender must show ported customers their effective blended rate before they sign — the weighted-average of the ported portion and the new additional borrowing. For our worked example (£180k at 1.85% plus £120k at 4.8%), the blended rate is 3.03% across the £300k total. That is what your actual repayment is calculated against, and it is what you should compare to remortgaging the whole balance at 4.6%. In almost every case in May 2026, porting wins by £150-£420 a month.
When porting is the wrong call
If your fixed term ends in under nine months, porting saves you very little — the lender will require a new rate selection on the additional borrowing portion that aligns to the existing fix end-date, which means a stub fix of six to nine months at a penalty rate (typically 0.5% above the standard tier). Better to wait and remortgage the whole balance fresh.
And if your move involves downsizing, porting often fails because the new property valuation falls below the loan-to-value bracket of your original rate. A £300k property with a £180k loan is 60% LTV; a £225k property with the same £180k is 80% LTV, which is a different rate tier and almost always disqualifies the port.