The UK fiscal year — termed the "financial year", ends on March 31 of the following calendar year. Thus, the UK budget for financial year 2011 would cover the period from April 1, 2011 to March 31, 2012 and is often referred to as 2011-12.
In the UK, the budget is often released in March of the previous fiscal year, less than one month before the beginning of the new fiscal year. Stopgap funding is provided by the Vote on Account (see below), and Parliament typically makes appropriations by the summer time. Legislative action on the proposed budget is faster in the UK and generally aligns with the executive's original budget request, since the Prime Minister's cabinet tends to exert significant control over Parliament (since the Prime Minister must have a majority in the House of Commons to retain power).
Governmental departments submit their funding requests — called "Main Supply Estimates" - to HM Treasury. The government then releases this data in a large consolidated document titled "Central Government Supply Estimates (Budget Year-Following Year): Main Supply Estimates" 
The UK government reserves the right to submit "Supplementary Estimates" in the winter and spring of a given fiscal year to update its agencies' spending totals for the current financial year and report any governmental re-organizations. When an agency submits a Supplementary Estimate, it is customary to also submit an "Estimate Memorandum" to the agency's relevant oversight committee in Parliament describing and justifying the changes. This condenses two functions - reporting supplemental spending requests and agency re-organizations.
Parliament is not expected to take action on a budget for the fiscal year until the summer, several months after the start of the fiscal year. For that reason, Parliament typically passes a "Vote on Account" in early spring that provides continuity of funding into the new fiscal year, up until the point that the new budget is enacted. The spending authorized in the Vote on Account is normally 45% of the amounts already authorized in the current fiscal year, taking into account the Main Estimates and any revised or Supplementary Estimates already approved by Parliament.