No, but it's definitely part of the solution. I'd rather some guy on a train have access to a large amount of undecipherable data that shouldn't be on the laptop than have access to it in plaintext.
Knowing what data should and shouldn't be on a laptop is a case-by-case decision, and given the number of government employees and how much of the data they have would be considered by someone-or-other to be important if it were lost (from the DVLA to your tax records to medical details etc) - it seems like these mistakes are inevitable, just by sheer force of numbers.
Which leaves government with three options:
1. Don't have any data that people care about (not going to happen)
2. Don't ever put data on laptops, or take laptops out of buildings (this makes it hard for the government employees to work from home, meet contractors etc, so there is a large cost associated with this. For very high value information - such as MI5, MI6 and the police etc, this is a good blanket solution that doesn't leave anything to chance or rely on Bitlocker)
3. Bitlocker everything. Continue to discipline staff who lose laptops, but at least this time when (rather than if) someone loses a laptop, the chance of the data being leaked to criminals, the press or the Internet is very much lessened.