What do you mean with "real impact"? There is no Hollywood-style super shock where everything goes to the dogs overnight, if you're looking for that. You're just losing investors over time, sector by sector. High security (and high volume) investors like communal pension funds, health insurances, etc. do not invest in unsound economies at all, for most of them it's outright illegal to buy anything but the best rated bonds. They're the first to get rid of their British government bonds. At the bottom the only ones left to ask for money will be shady speculators and gamblers, who estimate your risk and your interest rates in the double digit range. Not that Britain could survive that long. Every single percent point interest rate on the national debt costs 50 billion per year extra at the moment, tendency rising. As the undignified "Brexit Bill" debate shows, Britain is not exactly solvent. Only a little push in the right direction and the country will be caught in an inescapable debt spiral, left with the choice between a Greek style bankruptcy or a few decades of Japanese-style stagnation. As I wrote before, this doesn't happen overnight. It takes a few years, but it's perfectly foreseeable. The credit rating agencies already warned in 2015 and 2016, that a "yes" outcome of the referendum will damage the British economic outlook and credit rating and that a withdrawal from the single market will damage it even worse.