Before I saw your post and the one from liquorice I came across this site:
No you would not be able to use that as apart from the fact that you may reduce the optical signal level, you need specific optical cleaning kit to insure the connections are 100% clean.
Thanks for your replies.
I had already ordered, and received yesterday, a new external cat 6 cable to run where I was thinking they would have run the fibre so I don't need to buy anything else. and can now move my router to a more sensible, practical and convenient position.
Thanks again, you have all been very helpful, much more than those Openreach engineers were.
They are only Openreach Field Technicians, not engineers. Many would not have a clue and may even be sub-contractors.
Engineers design networks, and technicians build them.
I have just moved my router and the speed test is as good as it was before.
Thanks again.
This is the box outside https://youtube.com/watch?v=8cA1dJfNI_I&feature=shares
And this is the one inside
https://youtube.com/watch?v=4xxOukbj1D8&feature=shares