There were two options on the table, both had the same aim, to stimulate the the public into buying.
The idea of the VAT increase was so that shops could say "Buy now before the VAT increase" and that would get people spending again.
There was a debate within the treasury, and it was decided a decrease would stimulate the economy better than an increase.
The change in tax rate for high earners is mostly political rather than a serious money making exercise. It will only affect 1% of the population, which will please the other 99%. The rise is from 40%. In the 1980s the rate was 60%. High earners will not emigrate for tax reasons. People making large amounts of money employ accounts to find legal means of reducing their tax burden.
As has already been said, VAT hits the poor proportionally greater. As there are more people on lower wages than high wages, raising the many billions needed to pay back the Government's large borrowing from higher and higher VAT would be very unpopular, especially with an election in two years time.