Weeeee ....eeeellll....
I got it sorted!
Short story: it was to do with the accelerator. Most likely, leaving my Bongo unused in the damp weather, the connections or something for accelerator pedal got damp, and so that it why my bongo wouldn't move properly. The accelerator wasn't engaged at all.
Long story: I rang my breakdown company. I did have Homestart. But £30 excess charge to come out and take it on lorry to a car mechanic of my choice. I rang a local car mechanic I had been recommended in my area to ask him if he would be prepared to have bongo delivered to him. He suggested it simpler if he simply came out this morning to take a quick look first. He said straight away its the accelerator. He pressed it a few times
with the engine off, and (lucky!), that seemed to engage it again. I drove it around for about half an hour and all seems well again!
A little bit embarrassing, as it was quite a simple thing

really, as someone suggested!! But I panicked a bit and wasn't sure what to do.
Still: its an ill wind that blows no good. I have now found a handy local mechanic who knows about Bongos. He'll put a small charge for his call out I think when he does my MOT next week, so it hasn't worked out too expensive, or too much drama.
Second: the moral of the story - obviously - not to leave Bongo unused for too many weeks. Especially in damp weather. I think I read somewhere most vehicles, Bongos certainly, like to be used.
So, thank you all very much for your advice and suggestions, and I'm sorry if I took up your time and energy for my little drama. Hope to see some of you again soon. Am hoping to go to Wales meet up and Surrey one later this year.
Mary-Ann