Figures obtained recently by the local East of England  Liberal Democrats show that the tax burden on the lowest paid, under the Conservative/Liberal Democrat Coalition government, is lower as a proportion than it was under the previous Labour government. And those on the highest incomes are paying a greater share.
The information comes from the official HMRC (Her Majesty’s Revenue and Customs) web site. The link is:
http://hmrc.gov.uk/stats/income_tax/table2-4.pdf
In summary:
The share of total tax paid by the top 25%  was 71.5% in 2009-10 (The last year of the Labour Government)

The share of total tax paid by the top 25%  was 73.9% in 2011 – 12

The share of total tax paid by the bottom 25% was  2.7%  in 2009-10

The share of total tax paid by the bottom 25% was 2.4% in 2011-12

So the tax burden on the highest paid has risen under the Coalition and the burden on the poorest paid has fallen.

Note:
The Personal Allowance (tax free earnings before income tax becomes payable) rose in the 2011 Budget by £1,000 from £6475 to £7475, and is planned to rise further to £8105 from April 2012.
This is exactly as proposed in the Liberal Democrat manifesto at the last general election in May 2010.