AL_n wrote:
I'm not really a broccili fan, so I wonder if anyone suggest other
vegetables which would have a similar useful effect?

Potatoes are good at breaking down clay soil, I believe. Although I can't
really say anecdotally, as we also tend to pile loads of manure in the bed
pre-potato planting.

Pumpkins and courgettes could be good for smothering, with their giant
leaves. Beans will improve the nutrients in the soil for next year.