More interest in the interesting case of UK interest rates

In a recent blog Accelerating interest in the interesting case of UK interest rates we compared the level of the official Bank Rate, which has now been at 0.5 per cent for over seven years, with a representative unsecured borrowing rate. In doing so, we found some evidence that credit conditions might be easing following the credit market disturbance of the late 2000s. Here we take the opportunity not only to review that data again one month on, but also to see whether a similar picture is true for the mortgage market.

Theories of the financial accelerator argue that the macroeconomic environment can affect commercial banks’ lending practices. One way in which this can operate is through the difference between banks’ lending rates and the official Bank Rate. We can think of such interest-rate differentials – or spreads – as a credit premium. The size of the premium may be thought to reflect lenders’ perceived risk of default by borrowers. It is argued by some economists that interest-rate differentials will fall when the economy is doing well and increase when the economy is doing less well. This is because the probability of default by borrowers is seen as smaller when the macroeconomic environment improves.

The effect of interest-rate differentials that are contingent on the macroeconomic environment is to amplify the business cycle. For example, a positive demand-side shock, such as a rise in consumer confidence, which causes the economy’s aggregate demand to rise will, in turn, lead to lower borrowing rates relative to the official Bank Rate. This financial effect further stimulates the demand for credit and, as a consequence, aggregate demand and economic activity. It is an example of what economists called the financial accelerator.

The chart shows the Bank Rate along with the average unsecured borrowing rate on loans by Monetary Financial Institutions (MFIs) of £10 000. Unlike secured borrowing, which we consider shortly, unsecured borrowing is not secured against property.

As expected, we can see that the unsecured borrowing rate is greater than the Bank Rate. In other words, there is a positive interest-rate differential. However, this differential is seen to vary. It falls sharply in the period up to the financial crisis. In early 2002 it was running at 8 percentage points. By summer 2007 the differential had fallen to only 1.7 percentage points. (Click here to download a PowerPoint of the chart.)

The period from 2002 to 2007 was characterised by consistently robust growth with the UK economy growing by about 2.7 per cent per annum over this period. This may point to economic growth can contributing to an easing of credit conditions as implied by the financial accelerator.

The story from 2008 changes very quickly as the interest-rate differential increases very sharply. In 2009, as the official Bank Rate was cut to 0.5 per cent, the unsecured borrowing rate climbed to close to 10.5 per cent. Consequently, the interest-rate differential rose to 10 percentage points. Inter-bank lending had dried up with banks concerned that banks would default on loans. The increase in interest rates on lending to the non-bank private sector was stark and evidence of a credit market disruption.

The interest-rate differential for unsecured borrowing has steadily declined since its peak at the end of 2009 as the unsecured borrowing rate has fallen. This implies that credit conditions have eased. In March 2016 our interest-rate differential for unsecured borrowing stood at 3.8 percentage points, not dissimilar to levels over the past 12 months. Interestingly, today’s differential on unsecured borrowing is lower than the 6.5 percentage point average over the period from 1997 to 2003, before the differential then went on its pre-crisis fall.

Our second chart repeats the analysis but this time for mortgages. The representative mortgage rate is the average standard variable mortgage rate.

Unlike that for unsecured borrowing, the interest-rate differential for mortgages is fairly constant up to the financial crisis. The widely report credit easing in the mortgage market appears to have operated more through amounts lent rather than through price, as evidenced by rising mortgage advance-to-income ratios. (Click here to download a PowerPoint of the chart.)

The second chart shows clear evidence of a credit market disruption from 2009. Hence, the markets for secured and unsecured lending saw credit conditions tighten with interest-rate differentials rising markedly. However, it shows that the higher interest-rate differential for secured lending following the credit market disruption remains. So while the differential has fallen sharply for unsecured lending the situation is quite different in the mortgage market. In fact, February and March 2016 saw the mortgage rate spread at 4.17 percentage points which is an historic high.

Our interest rate data show that interest-rate differentials can vary significantly over time. This is important to understand when we are thinking about the relationships between the macroeconomy and the financial system. Significantly, the data suggest that interest rates on different financial instruments can behave differently such that differences emerge in the patterns of spreads over the official Bank Rate.

The evidence on UK mortgage rates suggests that the market remains affected by the financial crisis and the credit market disruption that arose. Although the level of mortgage rates is historically low – which tends to capture many of the headlines – this masks an historically high premium over the official Bank Rate.


Bank warns EU vote may hit growth as it holds rates BBC News, (14/4/16)
Carney issues a warning as interest rates are held Belfast Telegraph, (15/4/16)
Bank Of England Leaves Interest Rates On Hold Sky News, (14/4/16)
UK banks plan to boost lending to households but not firms – BoE Reuters, (13/4/16)
Mortgage rates reach record lows as threat of Bank Rate rise evaporates Telegraph, Tara Evans (1/4/16)


Bankstats (Monetary and Financial Statistics) – Latest Tables Bank of England
Statistical Interactive Database – interest and exchange rates data Bank of England


  1. Why would we expect banks’ borrowing rates to be higher than the official Bank Rate?
  2. How might banks’ credit criteria change as the macroeconomic environment changes? Explain your answer.
  3. As well as the macroeconomic environment, what other factors might lead to a change in the interest-rate differential between banks’ borrowing rates and the official Bank Rate?
  4. How would we expect a credit market disruption to affect the interest-rate differential?
  5. Explain how the financial accelerator affects the change in the size of the economy following a positive demand shock.
  6. Explain how the financial accelerator affects the change in the size of the economy following a negative demand shock.
  7. What is the impact of the financial accelerator of the amplitude of the business cycle?
  8. How might regulators intervene to minimise the effect of the financial accelerator?
  9. Why might explain the high interest-rate differential on mortgages that continues to persist following the financial crisis?
  10. Analyse the ways in which the financial system can stabilise or destabilise economies.