The U.K.'s new coalition government will deliver Britain's most important and painful budget in decades today, with a spending plan that is likely to define the fortunes of both the government and the country for years to come.

You can read our run-up to the announcement here, and follow our live coverage of the key points -- and market reaction -- as it unfolds here, from 12:30 p.m. BST (7:30 a.m. EST) Tuesday.The budget to be delivered by George Osborne today is expected to be extraordinary, in terms of the pain it's expected...