depends on what kind of meconopsis. Are they blue or the yellow/red nepaulensis type?

They are blue ones.

Having just visited the Himalayan garden in North Yorkshire where they have loads of blue, they leave all the seed heads on so they self seed. I have some in my garden and have tried both leaving them and removing so far no difference in flowering. They are short lived perennials and the gardener at the garden recommended dividing the plant every 3-4 years -in spring so next spring I'll be trying that. I am also going to try using a seed pod and sowing seeds next year.

Thanks. I did sow from seed last year. Tried some bought seed and seed given to me. They all germinated, but most failed. So, far I only have a single seedling left from 3 sets. I was hoping to use seed from one of the new plants, but having seen that video, it has now made me wary of leaving the seed heads on. So, I may skip it this year and try next.
Another point to make. One of the new plants was bought from a garden centre last month. It was in flower as was all their plants. So, if they do not survive after flowering in their first year, there is little use marketing them as perennials.