Hello Trevor,
many thanks for making the effort to respond. Apologies for not answering sooner. I appeared not to have a problem with the accelerator pedal. On the basis of reports on this forum I decided to assume that the problem was the suction control valve on the fuel pump and got Nissan to do the job for me. They agreed that that would have been their first choice as the cause of the problems I had i.e. random going into limp mode (temporarily cured by switching off to clear/re-boot and starting again) ultimately sometimes with only 5 miles between events, combined with 'hunting' between 750 and 1000 rpm at idle when cold. They quoted me £350 parts and labour but ultimately it cost me £412 because when they dropped the exhaust for access some studs sheared and needed drilling out.
The good news is that the problem appears to have been cured! Many thanks to all contributors whose experiences helped me.