Hodgdon 777 has now been reclassified as an explosive rather than a propellent due to changes in its constituents. Consequently, potential buyers must now hold an explosive certificate to acquire it. Here is a link to the Sussex Police website announcing the change which I would guess is repeated on other police licencing sites.

https://www.sussex.police.uk/advice/...-an-explosive/

You can still legally hold and use earlier 777 products prior to the announcement which are not affected by the change. The status of Pyrodex has not changed and remains classed as a propellant without the need for an explosive certificate to acquire. Although the licences are free, the storage updates requited still represent another hurdle to jump if you prefer to use substitutes rather than black powder. Another problem is that may dealers are now not stocking 777 due to its reclassification and consequent decrease in demand among previous users.

Brian