Many years ago on a gardening programme on telly, I can remember the presenter (may have been Geoff Hamilton) saying that clubroot is endemic in peat, so if you start your brassica seedlings in a peat based, multipurpose compost you stand a good chance of acquiring clubroot, and infecting your 'plot'.

Since seeing this we have always started our brassicas of in a soil-based compost, and have not been troubled.

valmarg