Last year i established an asparagus bed and on good avice have picked no spears this year, I now have about a dozen ferny plants about 1 mtr high maximum. I want to extend this half plot width across the whole allotment, will the crowns spread or can I divide them or do I need to grow or buy more plants / crowns

Dave

Don't disturb the existing plants as your wait will have to restart.
Get new plants for the extra area.

Morning Compo, as Peter said buy new plants, and try and buy top quality plants from a specialist grower, as they will be there for many years. So what may seem like a lot of money spent now, will pay themselves back many times over in the coming years.

I'd agree. We started a third bed off this year with crowns from the Isle of Wight which were so cheap! They've all produced spindly spears in their first year so I'm hopefull this will be a good future crop.