I sometimes have to go out for a large part of the day so am getting several diferent friends to come and take Bumble out for walks so i dont have to rely on one person all the time. Two friends have been and he has gone with them with no problems. Yesterday my friend J came to take him out and both times when she jangled the lead he fled back into the sitting room and refused to go with her which we both thought was very strange! 
I had a "eureka" moment at 5am this morning and realised what the problem was...........J is the one who comes when it is time to bath Bumble (two person job) I realised that Bumble associates J and the lead with having a bath. He only had one last Tuesday and so he wasnt taking any chances! 
We have decided that she must come round regularly so he realises that she doesnt just come to bath him, also she must walk him with me too!