Looking at their policies on wikipedia, they seem fairly closely in line with the Republican Party in the United States (minus a few extreme social positions):

Taxation: lower taxes, especially on corporations
Health: cutting waste, allowing vouchers (i.e., a private system)
EU: get the Hell out before it's too late
Council of Europe: quit letting those Eurotrash Leftists tell the UK what to do
Immigration: reduce it
Same-sex marriage: support civil unions (I personally support marriage but this is generally the Republican position at present)
Climate change: skeptical on scope of man-made change
Defense: stronger defense

The only thing I didn't include was their position on the monarchy since the US doesn't have one. However, I can't see how their positions are markedly different from US Republican positions. Why are they "populist" rather than "conservative" in your opinion?