In the main FaceBook app there should be a paper clip icon to the left of where you type the message. Tap that and you should get some emoji and other options. Choose Attach a Photo: or the Camera if you want to take one on the spot.
I don't have FaceBook Messenger, but I'd guess there is a similar icon for adding photos, emoji, etc.
Thanks so much. I have found it now and it works fine. I appreciate your promptness.
Alex
Whilst you are there, I have only just tried he video filming and shot 3 brief sections. Is there a way to link these to run as one, or is that a complex editing task?