traveling from Mexico the uk?

If anyone can help me out I would realy appreciate it . All flights leaving mexico to the uk stop in the usa, will I need a usa visa

Sorry, but the USA suspended the transit-without-a-visa program after 9/11. If you need a visa to enter the USA you will also need one to transit the USA. Go to www.state.gov and click on Travel & Business for more information.

However, you may be able to transit Canada without a visa - check with the nearest Canadian Embassy or Consulate to be sure: http://www.dfait-maeci.gc.ca/mexico-city/