I Endorse Almost Everything Alex Tabarrok Says Here
Project Syndicate: A Stimulus Opponent Who Can Actually Find His ---!

Tim Besley and Andrew Scott Have a Very Good Idea for Britain

Basically, it's that Britain create a Congressional Budget Office:

Time for independent fiscal policy committees: Plainly, a new device is needed to restore credibility to governments’ long-term public finances.... [T]he problem is that the budgetary process is not sufficiently transparent. A related problem used to exist for monetary policy, but substantial reform – especially creation of the Bank of England Monetary Policy Committee (MPC) redressed this, but reform of the fiscal process has been limited. Plainly this problem is not unique to Britain. The solution, as with monetary policy, is to institutionalise fiscal transparency and ensure the proper long-term scrutiny of public finances. Achieving this requires the creation of a politically neutral, expert body. To take the example we are most familiar with this could, the idea would be to create a body that would assess the UK’s fiscal position twice a year – about two months before the Budget and the Pre-Budget Report...

By symmetry, the U.S. should probably create a real Shadow Open Market Committee as well...