Be very careful bringing seeds in from Pakistan as they can unwittingly bring in teeny pests and microbes that can devastate plants here with no resistance. There are strict rules about it so contact DEFRA first.
Better to google for reliable, licensed sources for your seeds and there are plenty of Asian allotmenteers about from whom you could get more locally sourced seeds.
As for willow, there are all sorts of people growing willow for coppicing for various purposes all over the UK but especially in wetland areas so once you've checked it's OK to plant them, have a google for UK suppliers. Again, imported plant material is responsible for the Dutch elm disease that has wiped out millions of trees, the burrowing insects that are devastating horse-chestnuts, ash die back and now there's a new pathogen wiping out olive trees in southern Europe and working its way north. Best to buy local or from a nursery you know has a good quarantine policy for imported plants.