The British economy has slowed since Brexit. Interest rates are at an all time low and inflation has recently come under control. There are a few budget deficits the government is working on and people want to save instead of spend. All of these indicate a slowing economy. However, at present these are soft gloves in the boxing match to get Britain back in shape.
There was naturally going to be a hit to the economy. There are too many ties to Europe as the economic system was designed around the criteria set forward by the EU. However, as Germany rises in prominence many British will feel as though they are not fully respected within this system leading to more nationalistic sentiments.
One must consider the history of the British and how they pride themselves on their historical past. They were once one of the top, if not the top, nation in the world and have influenced global development. As the country struggles to regain a sense of strength and vitality it will seek to do so by falling back on traditions.
The delay in development won't be very long. One could make an argument for pro-EU and anti-EU but in the end they have the industry to recover. It won't be easy and there will be some economic turmoil in the process but eventually they are likely to get there as they create new strategies to compete on world markets.
This delay in development occurs because there are lots of interconnections between Britain and other countries. Redefining, breaking, and reconnecting through new contracts, law, and partnerships simply takes some time. In many cases it could take up to 5 years or more to really get back to full speed. If the British feel they want to chart their own course they certainly can but they must realize they will be making their mark in the world on their own without the support the EU offered.