The BBC sent 277 staff to cover Glastonbury last year
The BBC is not doing enough to show it provides the "best possible value for money" when covering major sports and music events, a report says.
The National Audit Office (NAO) looked at how much the corporation spent at six events including the 2008 Olympic Games, Wimbledon and Glastonbury.
The NAO said the BBC needed to tighten up the way it budgeted for such events.
However it added that viewers generally valued and enjoyed the coverage provided by the BBC.
Of the events investigated - which also included The BBC Proms, Euro 2008 and Radio 1's Big Weekend - the NAO found that five out of the six finished under budget, or no more than 1% over budget. Radio 1's Big Weekend went 5% over budget.
But the NAO criticised the BBC for not having "a clear view" of its total expenditure, as individual budgets were drawn up for separate media platforms.
The report also noted some missing paperwork, adding: "The BBC has told us the budgets for its coverage of the Beijing 2008 Games, Wimbledon, and Euro 2008 were approved at divisional level, but could not provide documentary evidence of this as the approval was not minuted."
It also determined that the corporation did not explore other cost options properly which limited "its ability to make informed judgements about its use of funds".
The NAO found that the BBC spent £111 million covering sporting and music events between 2008-9, and £246 million securing the associated rights to broadcast these events.
HOW MUCH DID THE BBC SPEND?
Beijing Olympics - £15.565m
Euro 2008 - £8.682m
Wimbledon - £4.217m
BBC Proms - £3.712m
Glastonbury - £1.737m
Big Weekend - £888,000
Source: National Audit Office. All figures are for 2008 events
Actual coverage of the sports events cost £91m, while the music events cost £20m.
The report also found that a higher proportion of money was spent on presenters and pundits for sports events, than on festivals and music events.
Between 2% to 3% of total coverage costs were spent on "talent" for music events compared with 6% to 20% for sporting events.
At the request of the BBC Trust, the NAO did not disclose the total costs for presenters and pundits for each event.
Amyas Morse, Head of the National Audit Office, said: "Given the current economic conditions, the BBC has not done enough to demonstrate that its coverage provides the best possible value for money.
"When the BBC decides that it wants to cover a major sporting or music event, it should carefully explore a range of options, and set down clear objectives against which it can measure its achievements after the event.
"Without that, the BBC will not convince licence fee payers that their money has been well spent."
Torin Douglas, Media correspondent
The NAO report gives the BBC a pretty clean bill of health - five of the six events came in within one per cent of budget. But it says there's room for improvement in ensuring value for money, and there are still examples for the BBC's critics to pick out.
Edward Leigh, the chairman of the Public Accounts Committee, has criticised an extra £250,000 spent on constructing a studio in Vienna for Euro 2008, because the one allocated did not have a backdrop of the city's skyline.
There are figures on the number of staff and spending on events such as the Beijing Olympics and Wimbledon, which some newspapers are likely to highlight - including a five per cent overspend on Radio 1's Big Weekend 2008.
The BBC Trust, which commissioned the report, says many of the NAO's recommendations have already been implemented.
Jeremy Peat of the BBC Trust - which commissioned the report - said: "The report finds that the BBC has succeeded in coming very close to, or under budget, for all but one of the major events considered.
"But it is also clear that there are areas for improvement, particularly with regard to approval and post-event review processes."
The BBC Trust said many of the NAO's suggestions had already been implemented by the BBC. In addition, it has asked the corporation to produce an action plan for the implementation of the remaining recommendations.
A BBC spokeswoman said: "Today's review not only recognises that these events are enjoyed and valued by millions of viewers and listeners but that the BBC has, for the most part, delivered these events within budget and with appropriate staffing.
"The BBC accepts and will now implement the recommendations made in the review to even better demonstrate that it delivers value for money," she added.
Edward Leigh, chairman of the Parliamentary committee of public accounts, criticised the BBC's spending on Euro 2008 - which included spending £250,000 on the building and operation of a studio in Vienna.
"Such a casual approach to spending licence payers' money does not sit well with the ferocious commitment to cost-effectiveness and full accountability demanded of the public sector in the present economic climate," he said.
The BBC said in response: "There is no inference in the report whatsoever that the BBC has been "casual" in the way that it spends licence fee money."
Commenting, Don Foster the Liberal Democrat Culture spokesman, said: "It is shocking that the BBC spent over £350 million on sports and music coverage last year without knowing whether this represented value for money or not.
"The BBC must urgently implement a proper system to test whether their budgeting for these events is correct to ensure that licence fee payers' money isn't being wasted."