Thanks very much Kieran. You are right it appears to be the socket used by the bedside lamp which triggered the trips - always about an hour or so after switching it on. Strangely not every day and sometimes tripped again in quick succession.
And the combination microwave is also a culprit - tested both by plugging in and sure enough the lamp was fine in another socket, and the microwave tripped after about 2 hours.
So will consider consumer unit eventually but it seems it works well as evidenced by the results? Thanks again, Michael