A flat tax encourages economic growth. When people are allowed to keep a higher percentage of their earnings they will strive to increase their earnings. This in turn leads to increased tax revenue for Britain. Because it is simply calculated, it will lead to tax prep savings and more savings in man hours.
Yes, flat tax would be beneficial for Britain, because it would allow tax processes and collection to be simplified. Applying varying rates based on income is a complex matter. Therefore, applying the same rate to all income rates would simplify the process. In addition to this, a flat tax would lessen the burden on the poor and middle classes, since they are the largest group by head count.
I believe flat tax rates are much easier to deal with and I am sure that Britain would benefit from this change. A flat tax makes filling and paying taxes easier and it also makes checking those taxes easier. This means that more tax money can actually go to the things that matter.
The idea of the flat tax -- that all people are taxed the same percentage of their income -- is in theory a sound one. However, in practice, it would never work and might even have disastrous consequences for a country like the United Kingdom. In fact, it might have the opposite effect than what is intended.