Who knows where this government’s credibility will be after next week’s exceptionally difficult budget By instinct and conviction, Rachel Reeves is a traditionally social democratic, centre-left Labour chancellor. When she delivers her budget next week, though, those qualities will be hard to discern. The reason for that is simple but powerful. She has become hemmed in on every side by avoidably tight commitments on taxation, spending and borrowing. Above all, however, she is hemmed in by Labour politics. It did not have to be this way. Reeves would have had a freer fiscal hand if she and Labour had…