Burman steering boxes use ball bearings to carry the load between the worm and sector. They also use loose ball bearings for the front and rear thrust bearings on the steering shaft. In total, there are 30-odd loose ball bearings in the box.
I'd bet that when you loosened the front plate, you dislodged one or more bearings. #1, I wouldn't drive the car that way for fear it might lock up or cause internal damage. #2, I suspect that the only way to fix it is to remove the box, disassemble it, see if a ball has come adrift, and put it back where it belongs.
Note that reassembling these things requires 5 or 6 pairs of hands. The only way that mere mortals can do it is to coat everything with heavy grease to hold the balls in place while you put it together. When you take it apart, don't let the balls fall out and disappear under your workbench.
Good luck!