This is an incredibly reckless move by Theresa May. It will harm the country for generations to come. Democracy was the no.1 argument for Brexit. 48% wanted Single Market access because they voted Remain. 52% wanted to leave so the Leave vote wins. Of those who wanted to leave, it was split between those who wanted Single Market access and those who didn't. If say 4% of the Leave voters wanted Single Market access then democracy says staying in the Single Market is what people want.
Brexit only spells trouble for the U.K. in coming years. Its new isolationist approach will not benefit the country, only a select few possibly, and the people will be wishing they hadn't voted for pro-Brexit candidates in the first place. In the modern-day global economy it is suicide to partake in isolationism.
The UK will no doubt be hurt by Brexit economically. However, let's not forget that it is one of the world's top tourist destinations, and that is unlikely to change. Imports and exports will be hurt, but not critically. Luckily for the UK, it had refused to implement the EU's euro currency, so that will soften the blow compared to what it would have been.
Britain is always stronger than the rest of Europe. They were foolish to want to sign on to Europe's problems in the first place. The pound has always been stronger than the Euro, and Britain is smart to want its own autonomy in order to deal with the problems that it faces today.