The UK has been highly successful in attracting foreign investment. This is due to the flexible economic policy, low level of regulation and cheap labour costs. In joining the euro it could discourage investors and cost the country jobs. Investment has actually risen since the establishment of the euro. Most inward investment comes from the US and is high technological industries which are insensitive to exchange rates fluctuations.
The UK has stronger trade links outside of Europe, especially with the US most of which is in dollars. We are also the biggest European investor in the US and they invest twice as much in the UK as the rest of Europe combined. We already are in the EU's single market, which means having the same currency will make little difference. The euro is unstable against the dollar and trade will suffer because of this. Our economy has moved closer to the US than the EU and this ha shown that the pound has remained stable against the dollar.
Employment The 'one size fits all' interest rate of the ECB will most likely damage the economy. There is no job advantage as it is being in the EU and the single Market which is an important factor not being part of the euro zone. The euro was launched in 1999, at this time the UK employment carried on falling and inward investment reached record levels. In the 1990's the UK created more jobs than the rest of Europe put together and in 2000 unemployment was at 6% compared to an average 10% in the rest of Europe.
The one interest rate is causing problems in Germany where the economy is in a slump and in Spain and Ireland where the economies are over heating and inflation rising. Both situations have an effect on employment, if these countries where outside the euro zone they could adjust their own interest rates and exchange rates to compensate.
Political The euro can also be seen as a political device not just economic. If the UK joins there will be great pressure for us to participate in more acts of union. Also on the political side, it has been said that independent central bank is unfair. Governments must be able to control the actions of the central banks because they have been democratically elected by the people, whereas an independent central bank would be controlled by a non elected member. Therefore there would be a considerable loss of sovereignty. Power would be transferred from London to Germany. This would be highly unwanted because national governments would lose the ability to control policy.
We are the 4th largest economy in the world. Inflation and employment are at their best levels for 40 years. We have achieved long-term stability and joining the euro will only destroy this. By opting out we will have more independence and will be able to follow a more national foreign policy. As a result we will be recognised as a major world player and have more influence abroad separate from that of the EU.