Hi buddy!
Sometimes there are seeds that can take longer than necessary to germinate. (In a personal crop, I had some seeds that germinated after 3 weeks).
Always be hopeful. Using the 'UFO' system for germination is always a good option because it keeps them in good germination conditions for a long period of time.
There may also be a problem in the way the seeds are preserved. If they are not well preserved by the seller or if they are kept in poor conditions during transport, the seeds may end up being sterilized by chance.
If the current situation caused by the brexit (fucking brexit) had not happened, I could help you. But at present, it is practically impossible to ship to the UK.
Sweet smokes,
Apolo