Now seems to be resolved - after much cost on helpline. Had to plug laptop into dlan, then it recognised laptop, then reset the device, then reconnect pc to dlan, then reconnect laptop to remote dlan - all seemed a bit experimental (so much for the plug and play) but pleased to say that it now seems to be working - for the time being at least
Nobody at devolo seems to know how or why - they just kept saying that everything I did at their instruction, and the results it gave, was not logical...!
But all's well that ends well - sorry I can't help by telling you what the problem was or how to fix it properly, just spend money ringing Germany!!