Thanks for the response. I contacted my insurance company this morning and got what I think is a workable solution for my situation. While the general terms of the policy limit in relation to unoccupancy would remain at 42 days, ie. the policy would not be changed, they would consider sympathetically an application for extra days cover. While I did not pursue the matter I did gather that there would be no extra cost.
They did have queries about my alarm system, the key holders and arrangements I put in place to look after the house while we are absent.