makers ’ panel, around 40 % of firms consistently identify brexit as a major source of uncertainty, with less than 20 % viewing it as unimportant ( chart 5 ). bank staff analysis of the results points to a drag of between 3 and 4 % on nominal investment growth since the referendum as a result of this uncertainty. for more detail on these mechanisms, see the box on “ factors affecting the prospects for long - term supply following the eu referendum ” on pages 29 - 30 of the august inflation report. it is also possible that actual or anticipated changes in institutional arrangements due to brexit might affect the outlook for net migration and therefore population growth. specifically, it has been at the top of the list for two years, falling back for the first time to second place in q1, with its place at the top taken by weak uk demand. for more information on the decision maker panel, see bloom, n. et al ( 2017 ), “ tracking the views of british businesses : evidence from the decision maker panel ”, bank of england quarterly bulletin, 2017q2. the bank ’ s 2018q1 agents ’ summary of business conditions includes the latest published results from the survey. all speeches are available online at www. bankofengland. co. uk / speeches chart 5 : brexit as a source of uncertainty aug - sep 2016 feb - apr 2017 aug - oct 2017 feb - apr 2018 share of respondents ( per cent ) not important one of many sources 2 or 3 top sources top source of uncertainty on the demand side, while brexit did not lead to an immediate fall in gdp, it is nonetheless exerting a drag. in addition to its effects on investment, it has had a significant impact on real household incomes and therefore on consumption. the main vehicle for this impact has been the fall in the exchange rate, which remains some 15 % below its pre - referendum peak. the rise in import prices caused by sterling ’ s depreciation has had a material and persistent effect on incomes : real household income has only risen by 0. 2 % in the seven quarters since the referendum, compared with averaged growth of over 1½ % per year in the five years prior to it ( chart 6 ). given that slowing in real income growth, you could argue that it ’ s surprising that households haven ’ t adjusted consumption even more. consumption growth has certainly slowed : it has averaged around 0. 3 % per quarter since the referendum, compared to

i have described. a critical assessment of why trust in public institutions fell is important, but questioning central bank independence is not the right approach – subjecting central banks to political influence is unlikely to make them more trusted. we know the economic argument – empirical evidence shows that political influence is more likely to lead to short - termism and make the central bank less effective in preserving price stability. but there is also a political argument – political influence does not necessarily mean stronger legitimacy, precisely because it is likely to arouse the suspicion that the central bank is politically motivated and may therefore deviate from its mandate for political reasons. so i would argue that independence does not weaken accountability, it strengthens it. accountability, in turn, ensures that independence does not lead to arbitrariness and that the 1 / 4 bis central bankers'speeches mandate is fulfilled. so, proper accountability arrangements strengthen the case for independence. and they reinforce each other as cornerstones of central banks ’ legitimacy and effectiveness. at the ecb, our monetary policy mandate is for the euro area as a whole. and when the governors of the national central banks ( ncbs ) attend the governing council meetings, they are not representing their respective countries. they are there in a personal capacity and represent the interests of everyone in the euro area. so it is appropriate that we are held to account at european level, while the ncbs explain monetary policy decisions at national level. importantly, explaining decisions is not synonymous with exercising accountability. in principle, where a competence, such as monetary policy, has been fully transferred to european level, accountability should be practised at that level. this ensures that everyone in europe has the same ability to hold us accountable through the same bodies, namely the european parliament, complemented by judicial review by the court of justice of the european union ( cjeu ). in other words, a single monetary policy requires single accountability, but in a multinational setting it can be explained through various channels. attempting to strengthen political ties to national political systems, “ renationalising ” accountability through the back door, if you will, would only risk undermining the singleness of monetary policy and threaten its independence. people and markets would end up suspecting that the ecb is responding to national interests instead of acting in the interests of the euro area as a whole. accountability during crises central banks played a key role in managing the crisis and implemented some controversial measures. understandably, this triggered a demand for stronger scrutiny. the ec