Thank you all for your encouragement and advice
@bags27 Thank you for the suggestion but I'm pretty sure you're right and I wouldn't be able to use them. I do have a supplier here available here in the UK, though, so that's sorted.
@MattKing Thank you. I wasn't aware about this speed business. I had watched some videos on youtube about stand developing Rodinal where he actually used FP4 at ISO 200 to good effect. I have always just used box speed in my development in the past and I'm not sure how to deal with this now. Should I decrease the speed if I use standard development times then? When you say slightly would you say around 1/3 - 1/2 stop ?